Module B Learning Outcomes

What are Common Treatments for Spodumene?

-Like many stones, spodumene can be heat treated to eliminate undesired defects. -Typically, the heating process will make faint greens and pinks more vivid.

What Current Science is Being Performed?

In-depth studies on gem corundum deposits really started in the early 1990's when some of the more famous localities (e.g., Sri Lanka) became politically stable enough to visit and other significant gem corundum localities (e.g., Madagascar) were becoming producers. Furthermore, the appreciation of gem deposits as significant economic ventures has also prompted more studies funded by business entities. Perhaps the most interesting current research on gem corundum are studies on isotopic and geochemical fingerprinting by geoscientists Gaston Giuliani in France and Tzen Fu Yui in Taiwan. In their studies, the oxygen isotope ratios, trace element geochemistry, and sometimes mineral inclusions of hundreds of samples from known locations were measured and documented. From this database it is becoming apparent that scientists will soon be able to pinpoint the region of origin and possibly even down to which mine site of any given stone.

Failure of Kimberley Process in certain areas

-There is still significant trouble in the diamond world because of the significant value and ease of smuggling diamonds -Cote d'Ivoire, Zimbabwe, and Venezuela are countries with imperfect track records relative to compliance with the Process -The process is more geared to monitoring large scale production from more significant sources (e.g., hard rock mines) and has difficulty addressing smaller artisanal scale operations. -Kimberley Process is not effective in countries with unstable governments where most mining occurs on an artisanal scale -Conflict diamonds still exist, especially in West Africa, Cote D'ivoire, DRC (Congo), Angola, South America/Venezuela -Kimberley Process is effective in countries with strong stable governments and small to large scale mining operations -KP statistics for West Africa reveal worrying trends. his trend suggests that authorities have no credible data for national production capacity. Guinea's statistics have exposed large discrepancies with trading partners for over four years running, but the government has not taken steps to reconcile these differences. -Signs of improvement in internal controls are apparent in the few KP participants who have stepped up enforcement measures in recent years, but as a whole the KP has failed to respond quickly and effectively to situations of concern, and to ensure that all of its members are compliant with the scheme's minimum requirements. We call upon India, the current Chair of the Kimberley Process, and all participants, to consider the following recommendations at the 2008 Plenary Meeting -Many problems with the Kimberley Process continued after the publication of Loupe holes documentary and a great deal of lobbying from groups like Human Rights Watch, Partnership Africa Canada, Global Witness and the Diamond Development Initiative -More diamonds sourced from conflict regions were making their way through the system as "conflict-free" -The largest issue was the certification of Zimbabwe diamond operations from the military-controlled Marange Region -There, several NGOs were claiming that the production of diamonds were fuelling corruption and violence -This along with the issues in Venezuela and Cote d'Ivoire pushed one of KP's founders, Ian Smilie, to quit the board of the KP in 2009 -Following suit after continuing controversy of conflict diamonds passing as conflict-free, the NGO Global Witness, officially removed its support in 2011 for the KP again -Martin Rapaport of the influential Rapaport group of companies continues to lobby the KP for better regulations and better definitions of what "conflict minerals" are in light of the "certified diamonds" from Zimbabwe -Although the KP has made great strides in regulating the trade of rough diamonds from conflict regions, it has recently been failing at upholding its core principles in the face of human rights violations in a few select countries -Despite the number of disputed countries being low, the scale of the problems and diamond volume are significant -For example, ~12 million carats of diamonds worth $645 million USD were exported from Zimbabwe in 2012 according to KP documentation -This information by no means negates the fact that the KP is still important, but it shows that it cannot be the only solution -At present, there seems to be no reconciliation as Zimbabwe continues to operate under the certification of the KP and the above mentioned parties continue to protest the efficacy of the KP

Magmatic

-Two general modes for the magmatically-related production of beryl are considered here: one where beryl grows in situ (from Latin meaning "in the place") from granitic magma and a second where Be is transported via magmatically-driven hot hydrothermal fluids (e.g., in what are later represented as "frozen" quartz veins) . -Fractional crystallization is the removal and segregation from a melt of mineral precipitates, which changes the composition of the melt. This is one of the most important geochemical and physical processes operating within the Earth's crust and mantle. -Beryl can crystallize in situ within an intrusive body (fertile granite) without being concentrated in any one place. When beryl is found in this type of environment, it is called interstitial or accessory beryl and is tightly surrounded by other minerals. Miarolitic cavities (open spaces resembling mini-pegmatites) within an intrusion can also host beryl, and crystals can be free standing in these pockets. Gem beryl from these types of in situ environments are mostly aquamarine, but goshenite and morganite can occur as well. -Hydrothermal fluids are very hot waters with large amounts of dissolved elements and compounds, such as sodium (Na), chlorine (Cl), silicon (Si), and carbon dioxide (CO2). -The source of hydrothermal fluids will define their composition; fluids sourced from granite can contain rare elements, such as Be, boron (B), lithium (Li), and fluorine (F). -Parent magmas that contain dissolved elements such as Be are often termed "fertile". -The hydrothermal fluid and dissolved elements can then be transported significant distances from their original source. -Veins of predominantly quartz will remain where these hydrothermal fluids once circulated through the rocks. This is the most important of the magmatic models for gem beryl formation and is especially important when the hydrothermal fluids interact with the host rocks. -Quartz is often found in veins that cut through rocks. -Typically, hydrothermal fluids are corrosive to their surrounding host rocks and cause a number of chemical reactions that change the minerals that come into contact with the hot fluids. This can release elements that were originally tightly bound in those minerals, allowing them to become part of the hydrothermal solution. If the released elements include chromophores, then different varieties of gem beryl can form. Specifically, if Cr+3 is present in the corroded minerals, beryl can then incorporate it into its crystal structure, forming emerald! Many emerald deposits can be explained by this geological model. -Hot magmatic fluids rich in Be and B form quartz veins with beryl and tourmaline -An unusual geological setting in the Wah Wah Mountains of Utah, USA, has produced the only known location of a saturated red beryl. There, rhyolite (a volcanic rock) hosts beryl found in vesicles (volcanic gas bubbles). The rocks are essentially an extrusive equivalent of a highly evolved granite with abundant Be and, uniquely, manganese (Mn). In one sense, the vesicles in the rhyolite are sort of like the equivalent of miarolitic cavities in granite. The red beryl crystals of the Wah Wah Mountains are typically only a few centimetres long and rarely produce material big enough for sizeable-cut stones, making them quite rare and very expensive!

Allochromatic Colours and the Transition Metals

-You may recall from Lesson 12.9 that colour in gemstones can be roughly classified into idiochromatic, allochromatic and pseudochromatic categories. You may also recall that we sort of stopped at that point of complexity. -However, now that we've studied corundum and beryl as well as their gem varieties, we're going to dive just a little bit deeper into the chemistry and physics of allochromatic gemstones. -In the case of beryl and corundum, both of these gem minerals can have a wide range of colours and in both circumstances the vast majority of the colour-causing phenomena come from the substitution of a transition element for aluminum! -For example, chromium substituting in corundum makes ruby and in beryl it makes emerald. But why then do emerald and ruby have such different colours if they are coloured by the same transition metal, chromium? -Let's restate the question: Why does Cr3+ substituting for Al3+ in Al2O3 (corundum) absorb mostly all but the red portion of the electromagnetic spectrum while in Be3Al2Si6O18 (beryl) it absorbs mostly all but the green portion of the electromagnetic spectrum? The key to the solution is through an understanding of crystal chemistry and crystal structures. Let's start by looking at the immediate local environment of the Al site in both gem varieties: -In ruby, Al3+ is in octahedral coordination with 6 oxygen atoms. -In emerald, Al3+ is in octahedral coordination with 6 oxygen atoms. OK, so why the stark difference in colour? Let's find out, but be sure to recall information from the lessons on crystal structure, element substitutions, coordination polyhedral, beryl and corundum (Oi, that's a lot!) Chromian Corundum (Ruby): -The bonds between Al and O in corundum fall into two distance groups of 1.855 and 1.971 angstroms and are quite strong, but show that the Al-O polyhedron is distorted (ie, not a perfect octahedron with all equal bond lengths). -The absorption profile of light for ruby from has two strong absorption bands centered at "violet" (~420 nm) and "green-yellow" (~570 nm) with a middle absorption low centered in blue that is moderately absorbing. At the red end of the spectrum (~625-700 nm) there is little absorption. The result is a strong transmittance in red and mild transmittance in blue, giving the classic 'Pigeon's Blood Red' colour. -Again, remember that violet is at shorter wavelengths while red is at longer wavelengths, and the higher the line on the graph, the GREATER the absorption (ie, loss) of light. Where the line is lower on the graph there is LESS absorption of light, leading to more TRANSMISSION of that wavelength of light. Chromian Beryl (Emerald): -So what about emerald? The bond lengths between Al and O in beryl (Be3Al2Si6O18) are all near 1.907 giving a relatively undistorted local octahedron compared to corundum (Al2O3), however the beryllium-aluminum-cyclosilicate crystal structure of beryl with all its complexity results in slightly weaker bonding than corundum. This effectively shifts the two main absorption bands we see in ruby to slightly longer wavelengths. The end result is that the two stronger absorption bands center on "violet-blue" (~435 nm) and "yellow-red" (~650 nm). Transmission, therefore, is localized in the green to blue-green region of the electromagnetic spectrum. Let's restate the answer: Ruby and emerald, although coloured by the same transition metal and with similar absorption patterns, have different colours because the absorption regions (and conversely the transmission regions) are shifted due to differences in the local crystal structure and bonding character of Aluminum to Oxygen in each mineral. Here are the two plots combined into absorbance (first figure) and transmission (second figure):

1) Pyrope

Also called Bohemian garnet, or cape ruby. -Its colour can be dark red, violet-red, rose-red, or reddish-orange, depending on its composition -Iron, chromium, titanium, and manganese all substitute in the structure, and are all colouring agents to some degree -manganese aluminum silicate -High-chromium pyrope can exhibit an alexandrite (colour-changing) effect -Its crystals are dodecahedral and trapezohedral, although it is most often found in rounded grains or pebbles -Pyrope is a high-pressure mineral found in metamorphic rocks and in very high-pressure igneous rocks such as peridotites and kimberlites -Large cut gems of more than 10 carats are uncommon because it is relatively widespread

Amber

Amber is fossilized resin, principally from extinct coniferous trees, although amber-like substances from earlier trees are known. -It is generally found in association with lignite coal, itself the fossilized remains of trees and other plant material. -Amber and partially fossilized resins are sometimes given mineral-like names depending on where they are found, their degree of fossilization or the presence of other chemical components. -Resin from the London clay and resembling copal resin is called copalite. -The world electricity is derived from the Greek name for amber, electrum. This is because amber can acquire an electric charge when rubbed, a property that is the most useful for identifying amber. -For several thousand years, the largest source of amber has been the extensive deposits along the Baltic coast, extending from Gdansk around to the coastlines of Denmark and Sweden. -It is both mined and recovered from Baltic shores after heavy storms. The largest single use of amber was the creation of the "Amber Room" in Catherine the Great's palace in Russia, a huge room totally lined and decorated with cut amber. Amber is said to represent the dividing line between individual and cosmic energy, the individual's soul and the universal soul. -It has been used to symbolize divinity, and a face the colour of amber is often seen on representations of saints and heroes. The Greek god Apollo wept tears of amber when he was banished from Olympus. -Most commercially produced amber comes from Russia, Poland, and the Dominican Republic but occurrences of amber stretch across the globe. -The amber of Russia, Poland and other countries around the Baltic Sea is considered "Baltic Amber". Amber is fossilized tree resin from conifers and some flowering trees that date back almost 345 million years ago. -Most of the amber of the Baltic region, however, is younger at ~35 million years old while that of the Dominican Republic is ~20 million years old. This material is thought to have been used since the 13th millennium BC both as jewellery and later as fishing buoys due to its low density. -One of the exciting features of amber is its ability to preserve insects and material from its original growth many millions of years ago (...the basis of the story for the movie Jurassic Park!). Ants, spiders, millipedes, and wasps, are among the many critters that have been found in amber, but lizards probably top the list in rarity! -Amber is Canada is uncommon, but the most significant occurences occurs in Late Cretaceous aged (~65 million years) coal formations at Grassy Lake, near Medicine Hat, Alberta. Secondary deposits of this same amber have been found downstream along the North and South Saskatchewan Rivers, accumulating in Cedar Lake, Manitoba. -One of the fascinating things about Canadian amber is that its age range spans across the Cretaceous-Tertiray mass extinction boundary, allowing scientists to look at trapped flora and fauna both before AND after the extinction of dinosaurs! Furthermore, McKellar et al (2011) investigated amber from Grassy Lake with postulated bird and dinosaur protofeathers! That paper is posted below for those interested. -Like most gemstones, there are imitations and fakes for amber. Andrew Ross of the Natural History Museum of London provides these four simple tests to help discern real amber from its fakes. Each test probes relevant physical properties of amber. Question A: Does rubbing alcohol make it sticky? NO Question B: Can it be scratched with a pin / nail?YES Question C: Does it float in a saturated salt solution? YES Question D: Does a hot wire produce a resinous smell? YES

Type I Diamonds, Ia, Ib

Type I diamonds have N concentrations greater than 10 ppm (and up to 3000 ppm) -Type I diamonds are further grouped into two: Type Ia where N atoms occur in aggregates within the diamond Type 1b where N in the diamond structure is dispersed (isolated single N impurities)

Idiochromatic

Idiochromatic minerals have inherent colours that are derived from essential elemental constituents of their crystal structure. The gemstone "peridot" (Fe2SiO4) is an example of a transparent idiochromatic gem mineral (forsterite) where Fe is the chromophore. Turquoise (CuAl6(PO4)4(OH)8·4H2O) is an example of an opaque idiochromatic gem mineral where Cu is the chromophore.

Other Quartz Gems

Smoky Quartz, Rose Quartz 7) Aventurine -Name given to a variety of quartz that has a spangled appearance due to sparkling internal reflections from uniformly oriented inclusions of other minerals> -Green aventurine is coloured by green fuchsite mica; brown aventurine is coloured by pyrite; and reddish-brown aventurine is due to hematite. -Other inclusions can colour the mineral orange, bluish white, yellow, or bluish green. -It is always massive 8) Cat's-eye quartz -Cat's eye is applied to two different minerals: one a variety of chrysoberyl and the other of quartz -When cut en cabochon, both show a single white line across the stone. -Cat's eye quartz is sometimes called Occidental cat's eye to differentiate it from the more valuable Oriental cat's eye - chrysoberyl. -Two may be distinguished by their specific gravities: chrysoberyl is much denser. -Cat's-eye quartz owes its chatoyancy (cat's-eye effect) and grayish-green or greenish colour to parallel fibers of asbestos in the quartz; a more reddish or golden colour derives from minute fibers of rutile. 9) Tiger's Eye -Semiprecious variety of quartz exhibiting chatoyancy -Tiger's eye is formed when parallel veins of crocidolite (blue asbestos) fibers are first altered to iron oxides and then replaced by silica -More opaque and has a rich yellow to brown colour -Major source is Griquatown West in South Africa 10) Rutilated Quartz -Takes its name from needles of rutile that are enclosed within it -Generally transparent, with any amount of needles from a few to so many that the stone may be nearly opaque -Needles can occur as sprays, or they can be randomly oriented -Rutile is generally golden in colour, but it can be reddish to deep red, appearing black without intense light. -The quartz can be found in well-formed crystals or in stream-rounded fragments 11) Phantom quartz -When gas bubbles or tiny crystals of other minerals accumulate on the termination of a quartz crystal during its growth, the colour of the crystal is subtly changed. -This can happen at several stages, leaving a "shadow" or "phantom" of the termination at each point -Green phantoms usually result from chlorite, reddish-brown from various iron minerals, blue from riebeckite, and white from gas or liquid bubbles or as a result of etching. 12) Chalcedony -A compact variety of microcrystalline quartz, chalcedony is composed of microscopic fibers -Can be mammillary, botryoidal, or stalactitic, and is found in veins, geodes, and concretions -It is white when pure, but much chalcedony contains trace elements or microscopic inclusions of other minerals, giving a range of colours. -Chalcedony that shows distinct banding is called agate -Chalcedony forms in cavities, cracks, and by replacement when low-temperature, silica-rich waters percolate through pre-existing rocks, particularly volcanic rocks. -Relatively porous, much commercial chalcedony is dyed. 13) Chrysoprase -Translucent apple-green variety of chalcedony -Colour derived from presence of nickel -The colour of some chrysoprase may fade in sunlight, and lighter coloured material might be confused with jade in cut stones -Most valued of the chalcedonies 14) Carnelian -Blood-red to reddish-orange translucent variety of chalcedony -Called cornelian as well -Colouration is due to the presence of iron oxide, and it can be uniformly coloured or banded -Strongly banded material is known as carnelian agate -Freshly mined carnelian is often placed in the sun to change brown tints to red 16) Sard -Translucent, light to dark brown chalcedony -Bands of sard and white chalcedony are called sardonyx -Sard forms from the deposition of silica at low temperatures from silica-rich waters percolating through cracks and fissures in other rocks 17) Bloodstone -Also known as heliotrope -Dark green variety of chalcedony coloured by traces of iron silicates and with patches of bright red jasper distributed throughout its mass -Both polished and unpolished stones show red spots on a dark green background, resembling drops of blood. 18) Jasper -An opaque, fine-grained or dense variety of cryptocrystalline quartz, jasper is related to chert -Chalcedony incorporating various amounts of other materials that give it both its opacity and colour -Brick-red to brownish-red jasper contains hematite; clay gives rise to a yellowish-white or gray, and goethite produces brown or yellow -Found world-wide wherever crypto-crystalline quartz occurs

Did ya know

The abrasive emery (such as those in your emery board) is actually a mixture of sand-sized grains of corundum and magnetite (Fe3O4). Historically, emery has been mined from regions with corundum hosted in marbles, just like some of sapphire and ruby mines of the world. Most notable are the emery mines of Greece located on the Island of Naxos, where the host rocks have been described as metamorphosed bauxite layers in marble. The hardness of corundum (Mohs = 9) makes it a perfect abrasive, as the only other common mineral that is harder is diamond!

Black

abundant graphite and other opaque inclusions

How Large Does it Get?

-A distinction must be made here between ordinary corundum and its gem varieties. Opaque, non-gemmy corundum crystals have been found in the "giant" size category. These huge crystals, measured in pounds or kilograms instead of carats or grams, have been found the world over in gemstone localities and also in areas that have no significant gem occurrences, just corundum. -A 312-lb crystal was reported to have been found in North Carolina in the mid-1800's. Other large crystals have been found, originating from Brazil (up to ~135 lbs) and Sri Lanka (up to ~85 lbs). The largest corundum crystal found to date is hosted in the Geological Survey of South Africa's Museum and weighs in at 335 lbs. It is from the Transvaal region, measures just over two feet in width, and is in the shape of a nice classical hexagonal dipyramid. -Examples of large sapphire and ruby gemstones don't get quite as large as ~300 lbs, but still reach some impressive sizes. Faceted stones tend to be smaller than those that are shaped into cabochons, as is done with many star sapphires and star rubies. -Most significant rubies are from Burma, and some from Sri Lanka -For sapphires, there are stones from Burma, Sri Lanka, Kashmir, and Yogo Gulch

Tweezers

-A simple tool, but necessary for anyone looking at minerals, gems or jewellery. A steady hand is tough to find, and even if you have one, the oils or sweat from your skin can alter the optical properties of the item at hand. -Gemstone-specific tweezers also have a couple of adaptations to facilitate investigation including textured tips (for grasping stones), small groves along the end of the tips (for a better grip of stones along their girdle), and locking mechanisms (so you don't drop a stone!). -Other gem specific tweezer tools are stone holders. They resemble a clicking pen with the point replaced with spring-loaded retractable prong claws and no stopping mechanism. They allow for a stone to be tightly held by more than two contact points, as with tweezers.

Rough Corundum and Cut Corundum

-As mentioned previously, most euhedral corundum crystals show a hexagonal growth habit forming squat plates or tapering "barrels". Often the crystals will show a modified growth habit or, if found in placers, will have their delicate corners worn away. The images below show this habit with varying degrees of modification. -In displaying the stone's vibrancy, the cut of sapphires and rubies is not as critical as that for diamond. However, a well planned cut will always make a stone exhibit the best possible colours and decrease the distracting presence of any inclusions. Light-coloured stones are often cut deeper to intensify colours. Deeply-coloured stones are often cut shallower in order to soften the colour. Stones that are cut too shallow display "windows" through the stone because much of the light entering will not be reflected back to the observer. If colour zoning in a specimen is present, a proper cut can hide the zoning, or if desired, emphasize it.

What Does Tourmaline Look Like Rough?

-As noted previously, most tourmaline crystals have an elongated crystal habit and often form in a nice euhedral shape. Crystals will often have striations (small grooves) down the length of the crystal. -During the last stages of pegmatite growth the environment can become quite acidic and corrosion of crystals can occur. Single crystals are common, as are "fans" of tourmaline consisting of many crystals growing simultaneously. Single crystals produce the best gem specimens.

Where is it Found Locally? (Pegmatites)

-Canada is host to numerous pegmatites, but none yet with gems like those seen in Brazil or the USA. Pegmatites occur in the relatively young Cordillera of Western Canada (BC, Yukon, NWT), within the Canadian Shield that makes up the majority of Canada's landmass, and on the eastern margin in the Appalachians. -Prof. Cerny of the Department of Geological Sciences at the University of Manitoba has been studying pegmatites of the Canadian Shield for decades. His publication on the subject in 1990 includes an extensive list of pegmatite sites between Manitoba and eastern Canada. In the Canadian Shield, the "Superior Province" is likely the best area for finding significant sources of gem bearing pegmatites. Within this area is Tanco Pegmatite Mine in southeastern Manitoba, an extremely evolved pegmatite that has been mined for its Li, Cs, and Ta ores for several decades. -The non-filled area (British Columbia and parts of Yukon) is the younger western Cordillera. Figure modified from the Geological Survey of Canada. L. Groat of the UBC Department of Earth and Ocean Sciences has been studying pegmatites in the younger Cordilleran rocks on the western side of the country. His publication in 1996 summarizes studies performed on a suite existing in Yukon and Northwest Territories. -Extensive pegmatite fields also exist in B.C. and many have been located in the Kootenay area. In his 2003 article (optional), J. Brown investigated the potential of pegmatite-related mineralization in this area with a focus on about a dozen individual occurrences. If you are a rock hound and looking to get out and about in southern BC, have a read! -There are a number of topaz and beryl bearing granites and pegmatites in the Canadian Appalachians, including the Brazil Lake Pegmatite and the coarse grained East Kemptville leucogranite. -Notable pegmatite-associated gem beryl occurrences include emerald at Ghost Lake in Ontario, goshenite at the Little Nahanni Pegmatite Group, and aquamarine throughout the Kootenays. Topaz associated in pegmatites have been located in Yukon Territory near the towns of Teslin and Swift River. -Tourmaline of the elbaite variety has been found in pegmatite from Northwest Territories and Quebec. Most exciting is gemmy tourmaline from the O'Grady Batholith, a remote area at the top end of the Nahanni River. There, multi-coloured crystals have been recovered up to 10 cm long and include pink, brown, green, orange, and blue colours. Other localities closer to Yellowknife include the Ryder pegmatite and a number of sporadic smaller pegmatite bodies. In Quebec, pegmatites near the Leduc mine are producing gem quality tourmaline, normally of pink and green colour. -So far, *no large gem quality stones have been produced from Canada's pegmatites* although some smaller material of high quality have been cut. With such a diverse geological framework in Canada under many different environments for pegmatites, it is only a matter of time until some fantastic finds are uncovered.

Where is Emerald Mined Globally?

-Emeralds are primarily produced from smaller operations in remote regions, typically in developing countries. Colombia supplies an estimated 60% of the world's emeralds with most of the reported balance coming from Zambia, Brazil, and Zimbabwe. Unfortunately, many of the countries that could produce emerald have unstable political environments and as a result unmonitored artisanal mining and smuggling is common. -Commercially produced aquamarine comes primarily from Afghanistan and Brazil, although Madagascar also produces significant quantities of gem beryl and is becoming a more significant global source.

How is Corundum Valued?

-Rubies and sapphires are valued primarily for their colour, then for their clarity. Since rubies and sapphires are treasured for their intense colour it is no surprise that this is the primary deciding factor for its value. -A nice clean stone is more attractive than one that is heavily included. Origin has a strong impact on the value of stones; size and cut are also important. -Stones originating from conflict zones or undisclosed locations are often undesirable to many consumers. Conversely, corundum sourced from historical locations are, in a sense, analogous to brand name items like Gucci or Armani. -When considering size, large stones are rarer. -For cut, a poorly faceted stone will not show its best colours and will likely have to be re-cut and therefore lose some carat-weight. So, like diamonds, there are 4+1 Cs to evaluating gem corundum: colour, clarity, cut, carat... plus Country of origin! -The best sapphires are valued according to the purity and intensity of the blue, with the "ideals" showing either refreshing cornflower blue or a velvety royal blue. Most of the highest calibre sapphires come from three different regions of the world. Stones from Kashmir are often the most valuable and exhibit an intense, velvet-like blue. Burmese sapphires are also highly valued for their saturated blue. Burmese stones often show wonderful asterisms. Finally, Sri Lanka and its cornflower blues, not to mention their very large sizes, are also prized. -Rubies with Pigeon's Blood red colouration, a colour described as a pure red with a hint of blue, are highly valued. Pigeon's Blood red rubies typically originate from Burma, but other noteworthy localities of high quality ruby are found in Vietnam, Sri Lanka, and Thailand. The highest quality rubies will show a strong red fluorescence and sometimes contain fine rutile silk that scatters the light across the stone, displaying a full bodied colour. Rubies with the finest optical qualities (colour, clarity) rarely have significant weights and a stone of ~2 carats is considered quite large. -The fancy sapphires (any colour of corundum other than blue or red) are more volatile in value and are driven by the consumer market place. For instance, fancy hot pink sapphires spiked in value over the last ~5-10 years whereas colourless, yellow, green, and orange stones have not received as much attention from consumers. One exception to this are Padparadscha sapphires that have an orange-pink colouration. These stones are known to have prices that approach the levels of fine rubies. -Once examined by a gemologist, rubies and sapphires will be ascribed a rating based on the 4+1 Cs. Ratings for coloured stones are less comprehensive than that for diamonds, and the five usual categories used are Poor, Fair, Good, Very Good, and Exceptional. In most jewellery stores, the top stones will be of "Good" quality. Very Good stones are found in high end stores, and Exceptional stones are found only in exceptional circumstances.

Labradorescence

-Labradorescence is similar to iridescence and is most commonly seen in labradorite, a species of the mineral feldspar. It is caused by diffraction of light interacting with very thin intergrown layers of calcium feldspar and sodium feldspar. The width of the thin layers defines the colour generated during diffraction.

What Does it Look Like Rough? (Topaz)

Topaz commonly occurs as well-defined euhedral crystals with sharp edges. It is stable in acidic geological environments, so it does not suffer the same resorption effects from a corrosive fluid as tourmaline and beryl do. -The lozenge shape is very common with flat tops, however, pointed terminations are not uncommon.

What is its Chemistry and Crystal Structure? for Topaz

Topaz's chemical formula is Al2SiO4(F, OH)2. The Si in the structure is tetrahedrally coordinated (has four oxygen anions around it) and the Al is octahedrally coordinated (has six anions around it). -What is unusual is that the anions of the Al octahedron is a mix of four oxygen and two fluorine atoms. Limited chemical variation is seen in topaz but some Cr has been noted in pink samples.

Slate

-A fine-grained metamorphic rock -Characteristic "slaty cleavage" allowing it to be split into relatively thin, flat sheets -True slates split along the foliation planes formed during metamorphism rather than along the original sedimentary layers -Its cleavage is the result of microscopic mica crystals that have all grown oriented in the same plane -Slate forms when mudstone, shale, or felsic volcanic rocks are buried and subjected to low temperatures and pressures -Common around the world is regionally metamorphosed terrains, such as the Appalachians, the Rhenish mountains, western Germany, and the Taihang mountains. -Slate occurs in a number of colours depending on the mineralogy and oxidation conditions of the original sedimentary environment -Black slate forms in oxygen-poor environment, red in an oxygen-rich environment. -Many slates are mottled or spotted -Fossils of plants and animals can be preserved in a slate -Slate is quarried in large pieces for use in electrical panels, countertops, blackboards, and

Describe the cleavage of diamond and its importance for diamond cutters

-Diamond has a set of IMAGINARY flat planes within its atomic structure that display perfect cleavage -Diamonds weakness is its cleavage -We describe these planes at being at [111], or a plane intersecting each of the three orthogonal axes at an equal unit of 1 away from the origin. -The shape of the intersecting planes is that of an octahedron (an eight-sided polyhedron), hence the descriptor of "octahedral" for its cleavage. -Four direction cleavage -Octahedral cleavage occurs when there are four cleavage planes in a crystal. -Diamond cutters require a good understanding of the mineral's crystallography and were its inherent weaknesses lie in order to expertly cute stones and grind the flat parts (facets) on a polished stone -Before the advent of analytical techniques using x-ray diffraction, info on the weakness of diamond were derived from observations that often came from gemstone cutters

Describe briefly the significance of emerald through history

-Emerald and aquamarine are two magnificent gems that are varieties of the same mineral, beryl -Both gemstones have been sought out and coveted for their beauty and properties throughout history -Beryl is colourful, hard, often transparent, resistant to many acids, and has the ability to form large crystals - all great ingredients for a gemstone -Beryl crystal structure requires the rare element beryllium (Be, atomic number 4) which only concentrates in very specific geological environments Emerald → vibrant green variety of beryl and one of the most valuable gemstones available, ranked in price with fine sapphires, rubies, and diamond -Its intensely vivid colour has been appreciated for millennia, as far as ~1500 B.C in the land that would become Egypt (they called emeralds "mafek-en-ma") -Emeralds are also known to have been coveted in ancient Greece (known as "smaragdos") with mention in Pliny's "Naturalis Historia", and have also been important facets of the Bible -It has been said that the very first emerald belonged to Lucifer -Exquisite diamonds are also well-known in ancient India and in more relatively recent times, South America -Colombia in South America is home to the most magnificent emerald -Ancient Aztecs used emeralds in much of their jewelry and some of their ceremonial items -The latin "smargdos" morphed to a Middle English "esmeralde", eventually to a spanish "esmeralda" and french "emeraude", and finally to today's modern English form, "emerald" -In ancient times, these various names were used for stones other than the current mineralogical definition of emerald, and included other green stones like peridot and malachite -With the advent of more objective tests, the mineral beryl became host to the official name of vibrant green emerald -In recent times, with the ease of access to non-destructive chemical and physical tests, the strict definition of emerald has again come under scrutiny -Many experts feel that green beryl with significant concentrations of the elements Cr and vanadium (V), but not Fe, should be called emerald -This narrow definition is still in debate as these definitive non-destructive techniques are commonly used in research and academia, but not accessible by the common gemologist or jeweller, and not to the general public -Emerald was synthesized in 1937 -Synthetic emeralds are currently manufactured in the United States, and appear very similar to natural crystals, rivaling them in colour and beauty -The world's greatest collection of natural emeralds is held in the Republic of Bogota Bank in Columbia -The largest crystal in the collection weights 1,795 carats -Emerald is a cyclosilicate, hexagonal crystal system, green, has a prismatic form, imperfect cleave, and white streaks -Emerald cut was specifically designed for emeralds to minimize loss of material in cutting -Emerald too cloudy to facet is polished into cabochons

Black and white light

-In both cases, if include all colour in subtractive colour theory, we will end up with Black, or the absence of colour. -Conversely, in additive colour theory if we include all colours we will end up with "White Light", or balanced light. White objects appear white because they reflect all colours. Black objects absorb all colours so no light is reflected.

Blue to grey

Blue to grey: Type IIb, Boron, Hope Diamond is this

octahedral cleavage

Octahedral cleavage occurs when there are four cleavage planes in a crystal. Fluorite exhibits perfect octahedral cleavage. Octahedral cleavage is common for semiconductors. Diamond also has octahedral cleavage.

Secondary modfication

Secondary shapes through increasing degrees of magmatic resorption. From left to right : 1) sharp edged primary octahedron (100% mass preserved); 2) octahedron with dodecahedral faces; 3) rounded dodecahedron with residual octahedral faces; 4) rounded dodecahedron (less than 55% of original mass preserved). (increasing magmatic resorption from left to right, from sharp to rounded)

Yellow to orange, subdued to intense, as well as almost colourless:

Type Ia, Nitrogen, Tiffany Diamond is this

Subtractive colour theory

- Cyan-Yellow-Magenta in subtractive. We'll focus on the Subtractive Colour Theory side. If we subtract the yellow portion of the electromagnetic spectrum we look across the diagram and will accordingly see a predominance of blue light. Similarly, if we subtract yellow and cyan (ie, green) we see a predominance of magenta (blue and red) light. Conversely, if we subtract magenta (blue and red) we see green. -It's also kind of like saying "yellow ink is really good at absorbing blue" or "yellow sapphire is really good at absorbing blue" and really good at letting the wavelength region centered on yellow reflect/transmit. Or, "magenta+yellow ink is really good at absorbing green+blue" or "ruby is really good absorbing green+blue" and really good at letting the wavelength region around red reflect/transmit. -The spectra on the right are examples of what the transmittance profile would look like for: (top) a magenta coloured material that absorbs in the green region, (middle) a yellow coloured that absorbs in the blue region, and (bottom) a cyan coloured material that absorbs in the red region.

Refraction

-Refraction is different from reflection. When light passes from one medium into another, its speed changes causing light to "bend" or change in direction. The degree to which light is slowed and bent relate to the differences in the refractive indices between the two media as well as the angle at which the light path makes with the medium.

How fossils are formed:

-A fossil is a remnant, impression, or trace of an organism that has lived in a past geologic age. -Some have been preserved in fine-grained sedimentary rock, such as limestone or shale. -The most common fossils found are of plants and animals that once lived in a sea or lake. -Typically, after an organism dies, the soft parts decompose, leaving only the hard parts - the shell, teeth, bones, or wood. Buried in layers of sediment, they gradually turn to stone

Loupe

-A loupe (pronounced loop) is also known as a hand lens, or a handheld magnifier, and is used by every jeweller, gemologist, mineralogist, and geoscientist. - The standard magnification power used is 10X, and this is what gemologists and mineralogists will use as a base tool for investigating minerals, grading stones, and examining jewellery. -A 10X power loupe will create an image 10 times larger than real life. -Most loupes are constructed as "triplets", meaning they have three lenses mounted together that minimize distortion of the transmitted image. After your "eye", the loupe is the next most important tool for collecting visual information.

Pearl

-A pearl is a concretion formed by a mollusk and consisting of the same material as the mollusk's shell, which is principally the mineral aragonite. -In addition to aragonite, the shell contains small amounts of conchiolin, a hornlike organic substance; together these are called nacre, or mother-of-pearl. -Mother of pearl/nacre = aragonite + conchiolin -The finest pearls are those produced by mollusks whose shells are lined with mother-of-pearl; such mollusks are limited to certain species of saltwater oysters and freshwater clams. -The shell-secreting cells are located in a layer of the mollusk's body tissue called the mantle. When a foreign particle enters the mantle, the cells build up more or less concentric layers of pearl around it to protect the mantle. -Baroque pearls are irregularly shaped pearls that have grown in muscular tissue; blister pearls are those that grow adjacent to the shell and are flat on one side. -Pearls are valued by their translucence, luster, play of surface colour, and shape. -The most valuable are spherical or drop-like, with a deep luster and good colour play. -In the jewellery industry, saltwater pearls are most commonly referred to as Oriental pearls; those produced by freshwater mollusks are called freshwater pearls. -Cultured pearls are those that have been grown on a pearl farm. A tiny sphere of mother-of-pearl is implanted in the mantle of the nacre-producing mollusk, which is then placed in the waters of the farm -The oyster forms a pearl around the tiny sphere, which is then harvested up to two years later. -Colour of pearls varies with the mollusk and its environment. -Pearl can be any delicate shade from black to white, cream, gray, blue, yellow, green, lavender, mauve. -Rose-tinted Indian pearls are particularly prized. -Pearls vary from the size of tiny seeds - called seed pearls - to one large baroque pearl that weighted 90 grams. -Some of the finest pearls are from the Persian Gulf from Oman to Qatar, the waters between India and Sri Lanka, and the islands of the South Pacific. -Mother of pearl is mostly calcium carbonate, it is very durable and can be used for utensils, and for ornamentation such as buttons and inlays. -Mother-of-pearl is more valuable than pearl (overall) -Pearls colour and water depends on the water it comes from -Pearls from Japan = cream or white with greenish tones -Persian Gulf = cream -Black or reddish-brown = Mexico -Sri Lanka = pink -Golden-brown = Gulf of Panama -Cultured pearls from Japanese and Australian waters are the most popular. -Freshwater cultured pearls produced in China represent 95% of the market. They are cultivated in mollusks belonging to Hyriopsis spp., and they occur naturally in white, grey, yellow, orange, pink and purple colors.

4) Andradite

-A type of garnet -Calcium iron silicate -Has several variety names, related to its colour -Yellowish variety is called topazolite, because of its resemblance to topaz -yellowish-green or emerald forms are called demantoid, or Uralian emerald -Black is called melanite -Other colours are brownish-red, brownish-yellow, and grayish-green -The green of demantoid is caused by the presence of chromium; yellow to black is due to titanium -Make spectacular gems with greater colour dispersion than diamonds -Commonly found with grossular in contact-metamorphosed limestone, and in mafic igenous rocks

Allochromatic minerals

-Allochromatic minerals do not have inherent colours, or at least not vivid colours, and require "impurities" to generate their colour. -Emerald (Be3Al2Si6O18) is an example of an allochromatic gem mineral where Cr is the impurity that acts as the chromophore (recall from Lesson 7 why Cr is not listed in the mineral's chemical formula). -The tricky thing with allochromatic minerals, however, is that you can't just "shove" chromophore elements into a crystal, as we learned in the lesson on minerals. There needs to be an atomic site where a chromophore can substitute for a pre-existing element that is similar in ionic size and electric charge (not too big, not too small, but just right - the "Goldilocks Principle"). - In the case of emerald, the base formula is Be3Al2Si6O18 showing that it contains Be (normally +2 charge), Al (normally +3 charge), Si (normally +4 charge), and O (normally -2 charge). Chromium, normally with a +3 charge, substitutes for the only +3 cation in the base formula, Al.

Type Classification of Diamond and Crystal Chemistry

-Although gemologists and jewellers typically group diamonds based on the 4Cs, scientists classify diamonds based on crystal chemistry variations. -The first subdivision in the scientist's classification scheme is based on the amount of nitrogen (N) that has substituted into the crystal structure.

Where is it Found Locally?

-Although not a commercial producer, Canada is host to a number of emerald occurrences, most of which occur in the Northern Cordilleran mountains of BC, Yukon, and NWT. A single occurrence is also present in Ontario. -The Ghost Lake emerald occurrence near Dryden in northwestern Ontario is associated with pegmatite (Be source) which has intruded schist (Cr source). Most of the emerald occurs at the contact between the southern and central limbs of the pegmatite and is associated with the minerals K-feldspar, plagioclase, quartz, phlogopite, and tourmaline. -At the Lened emerald occurrence in the Northwest Territories, limestone has been thrust over vanadium-bearing black shales. Emerald occurs in quartz veins with calcite which extend from the thrust fault and pinch out in the overlying limestone. It has been assumed that a nearby granite body is associated with the emeralds, but it has not been undoubtedly proven yet. -Emerald was discovered at Tsa da Glisza (formerly Regal Ridge) in the Yukon Territory in 1998. The emerald mineralization is associated with magmatic quartz veins with tourmaline and small pegmatites that intrude a Cr-bearing schist. Emerald occurs most commonly along the margins of quartz veins, but is also found within the quartz veins themselves, and in alteration zones that surround the veins. The emerald occurrence is underlain by a granite pluton, which is the source of Be-bearing fluids and the heat that drove the geochemical reactions. -Crystals of V-dominant emerald were discovered in 1989 at Red Mountain, near Stewart on the central coast of British Columbia. The emerald occurs as small opaque crystals with numerous fractures in narrow quartz veins with pyrite and calcite that cut volcanic rocks adjacent to a quartz-monzonite intrusion. -A new occurrence with no magmatic association was discovered in the Mackenzie Mountains of the Northwest Territories in the summer of 2007 and is the subject of current research at Laurentian University. These green beryl crystals are colored primarily by vanadium and share genetic similarities to the emeralds found in Colombia! The full significance of this occurrence is still unfolding. Another recent discovery (2012) of emerald in Canada is the Anuri occurrence, located in Nunavut where pegmatite is cutting Archean greenstone hostrocks. The pegmatite is supplying the required beryllium for beryl and the greenstone (a metamorphosed komatiite being explored for gold) is supplying the chromium for the green colouration. Currently, the emerald has only been encountered in drill core at depth so while the scientific significance is high, the economic significance has yet to be fully evaluated. In the United States, emerald is found in a few locations including Hiddenite, North Carolina, and the Unita Mountains of Utah. At Hiddenite, the emeralds are associated with pegmatites and in the Unita Mountains, the emeralds seem to share a similar genetic story to those of Colombia, although these occurrences have not been studied in detail. Other Gem Beryl Aquamarine and other varieties of gem beryl are also common in Canada, but again, are not produced commercially here. The Rocky Mountains of BC and up into Yukon are so jam packed with beryl occurrences that the list would be overwhelming! Furthermore, non-emerald gem beryl can be found in significant quantities in Manitoba, Ontario, Quebec, NWT, and Nova Scotia.

Gem Beryl in Secondary Environments

-Although not particularly dense, beryl's resistance to weathering and its high hardness means that it can also be found in secondary deposits concentrated through weathering processes. -There are three main types of secondary deposits, eluvial, colluvial, and alluvial. Below we discuss these and why gem beryl can be found in some of these deposition environments but not in others. Useful tools for inspecting secondary deposits are sieves and gold pans. A conical gold pan (also known as a "batea") is used extensively in South America and is also very good for separating minerals by density. -Rock can effectively be dissolved and removed over long periods of time without significant erosion from running water. (Recall the difference between weathering and erosion, page 29 of textbook.) -Minerals that are most susceptible to weathering will be dissolved and carried away first, and those that are resistant will be left over in the dirt. These "leftovers" are often called residual or resistant minerals and are concentrated where the original rock source was located. Thus, these so-called Eluvial deposits are best formed in tropical environments where weathering rates are high. Because these deposits have been transported the least distance from its original source, excavation is usually uncomplicated. However, targeting these locations requires knowledge of the underlying geology. -Eluvial = gem concentration via in situ weathering of bedrock, distance from source = proximal -Colluvial deposits normally exist as a fan of crystals or rocks migrating down a hillside, away from the primary source hosted in the bedrock. These types of deposits do not tend to concentrate residual and resistant minerals in great amounts, however, they do allow geologists to track gems back to their original source. -gem concentration via gravity driven transport, distance from source = medial -Alluvial deposits are the classic secondary deposits. They are formed from flowing water, normally in rivers but also in creeks and streams. In these environments, the flowing water will preferentially move lower density material (like quartz and feldspars) rather than higher density material. The end result is that the densest material gets "left behind" and is concentrated in bends or hollow depressions in the beds of rivers. These are also called placer deposits and are historically famous for their effective concentration of gold nuggets and diamonds! Secondary deposits of alluvial nature contain material that has been transported the longest distance from its original source. Beryl's moderate specific gravity (SG) of ~2.75 doesn't allow it to concentrate in alluvial deposits as effectively as gold (SG=19), diamond (3.5), or sapphire (4) do. Furthermore, emerald does not usually concentrate in alluvial or colluvial deposits as well as aquamarine because emerald's abundant internal inclusions cause it to fracture more easily during transport. Eventually, only small fragments too small to be of economic interest will eventually remain. The gem placers (alluvial deposits) of Sri Lanka and the eluvial gem deposits of Brazil are two notable localities of significant secondary deposits of beryl where durability plays a more significant role than specific gravity (density). distance from source = farthest/distal -gem concentration via fluvial transport and density sorting

Ammolite

-Ammolite is both a relatively "new" gemstone and one that is produced almost exclusively from Canada. -Discovered along the St Mary River in southern Alberta (near Lethbridge) during the early 1900's, it was not brought to the international gem market until the early 1980's. Similar material has been reported from Austria and Madagascar, but neither of these locations produce the quality or quantity of ammolite from Alberta. -Similarly, the geological formation that hosts "ammolite", the Bearpaw Formation, extends into Saskatchewan to the east and down to Montana and Utah to the south. -The Bear Paw Formation is described as dark grey shale (see page 61 in your textbook) with layers containing numerous siderite concretions, competent round-shaped rock patches within the more fissile shale that envelope the ammonite fossils. -The Bearpaw Formation itself is ~230 m thick, however, only two thin horizons (~2 to 3 meters thick) have ammolite and are known as the K Zone and Zone 4. -Two main companies produce ammolite today, Korite International and Aurora Ammolite Mining and minor artisanal mining is also carried out. -The gemstone ammolite is the fossil shell of an Upper Cretaceous (~70-80 million years old) ammonite and is therefore considered an 'organic' gemstone even though this critter died many many years ago. The specific species of extinct ammonites that make up ammolite are Placenticeras meeki, Placenticeras intercalare and to a lesser degree, Baculites compressus. -These mollusks were similar to today's nautiloids and were once very common invertebrates that lived in the world's oceans. In fact, they were so prolific that their presence in a fossil record is used to deduce that rock's age and correlate it to other rocks. -In order for fossilized ammonite shell to display the vibrant colours of ammolite, the original nacre of the ammonite's shell must be transformed to the mineral aragonite. -This happened naturally over geological time as the sedimentary formation underwent increasing pressure and temperature. -The colours we see are produced through interference effects of light as a result of very thin layers of aragonite. Different thickness' of aragonite lead to different degrees of interference and therefore different colours. -Thicker layers of aragonite produce interefence colours of red and green, while thinner layers of aragonite produce interference colours of blue and violet. -The ammolite industry divides ammolite into 2 categories: Type 1 (fractured) and Type 2 (sheet). -Type 1 is the most common and represents smaller fragments of ammonite shell, now ammolite. -The more desireable Type 2 is more rare and represents larger portions of intact or barely fractured ammonite shells. -Because of the different genesis of Type 1 and Type 2 ammolite, they also show different microstructures (Type 1 is shingle-like, Type 2 is sheet-like) and have different competencies. -Consequently, the more competent Type 1 ammolite does not require stabilization by epoxy while most Type 2 material undergoes stabilization before use in jewellery. -Ammolite grading is not standardized like diamond, however, top quality ammolite is defined by a greater number of colours present in a single piece as well as how vivid those colours are. -Because ammolite is actually the mineral aragonite (page 180 in your text), it is quite soft and not suitable for jewellery 'as is'. -Ammolite is therefore often manufactured into doublets and triplets. These are composite gems with different layers. -Doublets have two layers; the bottom is ammolite and is capped by a harder and transparent top -material, such as clear quartz, spinel or corundum. Triplets are similar, but also have a third layer on the back, usually a very dark material like jet or dark shale to provide a deeper saturation of colour as well as to provide durability. Sometimes, doublets can also comprise a composite plus the ammolite and not have a top cap. Rarely, ammolite is sold 'as is' without any extra backing or capping - these are called 'naturals' and are usually displayed as specimens rather than in wearable jewellery.

Describe the 4 (four) main geological settings/genetic models for gem beryl

-An attempt to classify beryl deposits based solely on economics might result in two categories, those related to pegmatite and and those not related to pegmatite. (Recall your reading on pegmatites, assigned for Lesson 5, on page 36 of the textbook.) This scheme, however, neglects to consider the great diversity of environments in which gem beryl deposits can form. Nevertheless, for the sole purpose of finding gem beryl, this type of approach would likely yield the largest number of positive results since pegmatites are relatively easy to identify in the field and can host many other gemstones, too. A search for pegmatite-hosted gem beryl may not result in the best value of gem beryl, however, because the most valuable and rarer gem beryls are often found in unusual environments. -An efficient way of finding and studying beryl deposits (and all other gem deposits for that matter) is by identifying the source of the necessary components, understanding subsequent transport mechanisms, and by defining the events that cause deposition (or crystallization). Because gem beryl requires the element beryllium in its crystal structure, a search for beryllium is a good way to find gem beryl. - In the next sections, we will learn more about the geological models of beryllium enrichment, namely 1) pegmatitic 2) magmatic 3) metamorphic 4) secondary which can lead to the crystallization of gem beryl. -In searching for gem minerals, we must recognize the requirement of a favourable growth environment to produce stones that are sufficiently large and transparent to semi-transparent to be considered for faceting into cut gems. -These two variables further restrict the environments in which gem quality beryl is found. For larger crystals, one must typically have open space cavities or robust growth within a solid rock. For clarity of a stone, a stable and nurturing growth environment is also important. Although important considerations, these aspects of gem deposits are obviously less critical than finding an occurrence in the first place!

What is a 'conflict diamond'?

-An uncut diamond mined in an area of armed conflict and traded illicitly to finance the fighting. -conflict diamonds are diamonds illegally traded to fund conflict in war-torn areas, particularly in central and western Africa. The United Nations (UN) defines conflict diamonds as "...diamonds that originate from areas controlled by forces or factions opposed to legitimate and internationally recognized governments, and are used to fund military action in opposition to those governments, or in contravention of the decisions of the Security Council." These diamonds are sometimes referred to as "blood diamonds."

Anisotropic medium + Double Refraction

-Anisotropic minerals are those that exhibit more than one refractive index. -Materials that belong to the tetragonal and hexagonal crystal systems have two distinct refractive indices and those of the monoclinic, triclinic, and orthorhombic systems have three distinct refractive indices. -The orientation of these refractive indices is related to the unique crystal structure of each mineral, and the absolute difference between the refractive indices is called birefringence, Δn = n1-n2 birefringence = refractive index 1 - refractive index 2 -A result of this anisotropy is that light entering an anisotropic medium will be split into two distinct light rays. -In media with a high birefringence, the difference between the refractive indices is large and the difference in lights paths is significant. -Consequently, light transmitted through the medium appears "doubled" (see figure below). In media with a low birefringence, the difference between refractive indices is small and the difference in lights paths is minimal; consequently the resulting image looks more blurry than doubled. -Titanite is a rare gem mineral (but common mineral) that has a high birefringence (Δn = ~0.105) and in this photo you can see the doubling of the gem's rear facets. If you were to see this optical effect in a gemstone, no matter how subtle, it means the gemstone is anisotropic (ie, has more than one refractive index and is NOT isotropic). Titanite also has decent dispersion and although this idiochromatic gem has a strong green colouration, some 'fire' can still be seen near the center-left of the gemstone. Photo courtesy of Smithsonian Institute.

Colour wheel subtractive theory

-Another (sort of simpler) way of looking at this is via a colour wheel. You look across the wheel from the colour you are absorbing that will be roughly your end product (ie, if you subtract/absorb blue you'll get yellow). -The following figure is a classic "colour wheel" used in complementary colour theory. The core includes three primary colours (yellow, blue, red), which is surrounded by combinations to generate secondary and tertiary colours. -In complementary colour theory we often use these wheels to predict what colour will be produced when mixing pigments. Pigments are based on subtractive colour theory whereby their components will absorb certain portions of the electromagnetic spectrum and some classic opaque gemstones, such as lapis lazuli (also known as ultramarine), have been used as pigments through antiquity.

and aquamarine

-Aquamarine is the light to dark blue variety of beryl, and often has a delicate green tone, hence its name that alludes to the colour of the sea -The most coveted colouration of aquamarine is an intense deep blue, which is considerably rare than sky blue or "sea foam" colour that most people are familiar with -Aquamarine is also entwined with ancient history -Reference to these blue stones is made in ancient Egypt as well as in ancient Greece -Compared to emerald it has not received the same volume of attention -It has been suggested that the large clean stones we are familiar with today were likely quite rare through history -The absence of large magnificent aquamarine crystals diminishes its space in ancient history and lore -Aquamarine → "sea water" -Universally found in cavities in pegmatites or in alluvial deposits, and forms larger and clearer crystals than emerald -One transparent crystal from Brazil weighed 110 kg -In the 19th century, sea-green aquamarine was highly valued -Today, sky-blue crystals imparted by traces of iron are preferred -In ancient times, aquamarine amulets engraved with Poseidon were thought to protect soldiers -When cut en cabochon, some aquamarines show a cat's eye effect -Rectangular step cuts are used for aquamarine to show off the deep blue colour often -Prismatic crystals like those of aquamarine are often cut in squares or rectangles to preserve the gemstone material -Faceted mixed cut/ oval mixed is used to deepen the colour of the stone

Describe trends in diamond pricing based on differing clarity, colour, and carat size.

-As with grading reports, pricing reports are also made available for the diamond and jewellery industry by many institutions -Of these, the Rapaport is perhaps the most commonly used summary of current diamond prices -The prices (in U.S$1,000) are considered wholesale based on asking prices at New York firms and as a retail consumer, you would probably expect to pay double this -Many dealers buy stones at a discount from the "Rap" price -Other variables that must be considered are the number of stones you buy at a time, the type of jewellery the diamonds are to be used in, and whether the pieces are to be specially designed Clarity pricing: In the graph above, note the dramatic jumps in prices for G and better colours from IF - VS1, but not for colours H and worse. -This pricing trend is a result of high demand for clean stones of good colour. -In other words, for clean stones (VS1 and better), a good colour (G and better) is considerably more important (and noticeable) than for dirty stones where an off-colour is not a big deal against its many inclusions. -Also note the small price difference between E and F colours. This is because of the difficulty in noticing the slight colour difference. Now ask yourself, since D colour is close to E, why would it demand such higher prices? For worse coloured stones, the change in price with clarity is smaller Each colour category experiences a dramatic rise in price per carat leading up to ~5 carats. -Beyond that, a similar trend would make the cost to the consumer unsustainable. -The larger stones (10+ carats) are also less common and tend to only appear in specialty shops. -For the retailer, a large stone sold at a bit of a discount would generate the same profit as that for a smaller stone sold without discount. -For 0-1 carats, the price diff is not that significant for diff colours -Above 5 carats, there is stil a rise in price per carat but less dramatic, but D colours are still a lot more expensive than G, and then K (least expensive) -The graph above is the same as the previous one but with a closer look at the "smaller" stones. -Note that the steepest rise in value for a diamond occurs in two places: leading up to the 1 carat range and leading to the 0.5 carat range. This is a direct relationship to demand from consumers that want stones close to these "benchmarks". Note, too how on the low end of the scale, the differences in price per carat for the various colour grades are very small.

Asterism

-Asterism describes a prominent star shape that normally occurs as a six pointed star (although 4, 8 and 12 are possible) and is due to crystallographically oriented mineral inclusions in the host mineral. Gemstones with this characteristic are best cut as "cabochons" (shaped and polished as opposed to faceted) to show off this optical effect and the most famous examples are in sapphires and rubies.

Common treatments for Corundum

-At any gem corundum mine, most of the material found is not of gem quality. As a consequence, much effort has been directed to improving the quality of mined stones ever since mining of corundum began. -Almost all (~99%) sapphires and rubies are heat treated to change colours, intensify them, and increase clarity. -The robust nature of corundum and the mineralogical changes that occur when heat treating corundum are quite favourable. -The solid inclusions that detract from a stone's clarity (although some, including me, would argue that these add character to a stone) are usually comprised of elements that, coincidently, can be incorporated into corundum's crystal structure. -These inclusions are commonly rutile (TiO2), spinel (ideally MgAl2O4, but often "impure"), and iron titanium oxides such as ilmenite (FeTiO3). -Corundum's melting point (~2000 °C) is higher than most of its common inclusions. Thus, heating allows the solid inclusions to resorb or "melt" back into the corundum's crystal structure without melting the corundum. -Heating improves clarity by "removing" the opaque inclusions, but also by allowing chromophore-type elements, such as Ti and Fe, to become part of the corundum crystal and help colour the stone. Under the right conditions, Fe can be chemically "persuaded" to acquire a charge of either +2 or +3 which will also affect the resulting colour. -Fluid inclusions and fracture-type inclusions won't add to a stone during heat treatment, but these features can be annealed or healed to make them "disappear". Consequently, the clarity of the treated stone can increase dramatically. -Corundum also commonly undergoes diffusion treatment where an element not associated with the crystal is forced into the structure via heat, pressure, and chemical gradients. This allows the "treater" or chemist, to impart a variety of colours to the original crystal. Diffusion is most commonly used to change colourless sapphires into Padparadscha sapphires with the diffusion of beryllium (Be). -Treatment to corundum is typically done to rough stones that have not yet been cut since exposure to the high heat can also cause new fractures to form. Otherwise, a faceted stone could lose considerable value if it broke during the heat treatment process.

What Colours can Spodumene Have? How are These Colours Generated? What Gem Varieties Result?

-Kunzite (pink) and hiddenite (green) are the two main gem varieties of spodumene, however, some light yellow material has also been produced and is called triphane. -As with emerald, hiddenite has Cr as its chromophore. Stunning electric green specimens have come from Hiddenite, North Carolina, and the Kabul region of Afghanistan. -Kunzite's colour, as with morganite, is owed to trace amounts of manganese (Mn). This gem variety is much more common than hiddenite and is found the world over, although those originating from Minas Gerais, Brazil and the Kabul region of Afghanistan are considered premium stones. -Rarely, some spodumene will show hues of both pink and green. Polarizing filters can be used to filter out light vibrating in certain directions, allowing observations of the different pleochroic colours, as in the images below.

Apply the scientific method to identify an unknown mineral

-Because of its prismatic hexagonal nature, rough beryl crystals can sometimes be confused with quartz at first glance. However, beryl (hardness, H=7.5 to 8) is harder than quartz (H=7) and usually has flat crystal terminations rather than culminating to a point like quartz does. -Beryl often has striations parallel to the length of the crystal, whereas striations on quartz crystals will run perpendicular to the length of the crystal. -Beryl tends to exhibit basal cleavage and uneven fractures, while quartz commonly exhibits conchoidal fracture. -However, there are many non-destructive ways to find out whether your crystal is beryl other than smashing a chip off! -Depending on the specimen, beryl can also be strongly pleochroic (showing two different colours) when looking parallel and perpendicular to the long axis. -Aquamarine is sometimes difficult to distinguish from blue topaz but specific gravity aided by refractive index can rule out this similarly coloured stone. 1) Compile observations: Making detailed unambiguous and clear observations is vital to any scientific investigation whether that is recording results in a laboratory or describing the geology and mineralogy of a rock in the field. Our initial observations: The mineral is pink, fractured, non-transparent, and has hexagonal habit, vitreous luster, and poor cleavage perpendicular to its c-axis. 2) Form a Hypothesis: This is a provisional theory to explain the observations made. Our provisional hypothesis: This mineral is either corundum, beryl or possibly apatite (check your textbook!). 3) Test the Hypothesis: Procedures or tests used to collect data in order to determine if the hypothesis is correct. Our tests: Because the mineral is contained within a rock we are limited to testing hardness, streak, cleavage, luster, and habit. If you need a refresher on these properties, please refer to L7 or and your textbook (pages ~92-95). Our results: Hardness = 7.5, Streak = white, Cleavage = poor & perpendicular to the c-axis, Fracture = conchoidal, Luster = vitreous, Habit = tabular & hexagonal Our conclusion: Comparing these properties to those of corundum, beryl and apatite, it is apparent that the hardness = 7.5, cleavage = poor perpendicular to the c-axis, and luster = vitreous are characteristic for beryl and not corundum or apatite. However, the streak, fracture, and habit are characteristic for the three minerals. 4) Repeated testing, if needed, on the hypothesis will aid in enhancing the confidence of your conclusions. Do you feel that our test results confirm or reject the hypothesis that this is beryl? What other properties could be tested to support or reject the identification? Is it possible for all of these minerals to occur in granitic host rock? If this mineral was gem quality, what would it be called?

How is Topaz Valued?

-Because topaz is found in relatively large crystal sizes and responds well to irradiation treatment, prices per carat tend to be low for the more common varieties. -Blue, colourless, and brown topaz for example, are usually valued around $10 - 25 USD / carat. Especially large samples will naturally, command a higher per carat price. -Rich orange-red Imperial topaz is much less common and untreated stones of this variety normally range into the ~$1000 USD / carat for larger (~10 carats) stones. Pink to red topaz, which is even more uncommon, retails for up to ~$3500 USD / carat and rarely achieves sizes beyond 5-6 carats.

Describe the diagnostic properties of gem beryl (e.g., hardness, refractive index, SG, habit, cleavage, fluorescence)

-Beryl is an aluminous beryllium cyclosilicate (Be3Al2Si6O18) that commonly forms hexagonal prisms with flat "basal" terminations, and less commonly more squat tabular prisms. -It has a hardness of 7.5 to 8 on the Mohs scale, and is colourless when pure. -A basal cleavage (poor) is present and fractures are described as conchoidal to splintery. -Specific gravity of beryl ranges from ~2.6 to ~2.9, with variations due to element substitutions. -Similarly, the refractive index of beryl ranges from 1.57 to 1.61 depending on its composition. -Long and shortwave UV fluorescence can also be observed in beryl, and is most commonly ascribed to the presence of trivalent chromium (Cr+3), which produces a red hue. -The pink variety of beryl, morganite, will also fluoresce in UV light and commonly shows an orangey-pink hue. -Fluorescence in UV light is one of the amazing features of Cr-bearing beryl. It means that not only does the stone reflect the Sun's visible light, but it also emits extra light when impacted by light in the UV range.

Gem Beryl in Pegmatitic Environments

-Beryl is common in granitic pegmatites and its gem varieties (i.e., aquamarine, heliodor, morganite, and goshenite) are typically found within rare-element-enriched pegmatites. -Rare elements common in these types pegmatites include lithium (Li), cesium (Cs), tantalum (Ta), niobium (Nb), Be, and sometimes yttrium (Y) and fluorine (F). -Pegmatites can also exchange other elements from the "wall rocks" that they intrude into and come in contact with. -Commonly, this is how non-pegmatite related elements, such as Cr and V, are introduced into these rocks which then allow ever more rare mineral and gem varieties to form (e.g., Paraiba tourmaline and emerald). -Pegmatites typically have a concentric structure, similar to the layers of an onion. -The zones, listed from outside inwards, are called Border, Wall, Intermediate, and Core (see figure below). -Beryl has been found from the Border Zone to the Core, but the highest quality crystals (i.e., large size, good transparency, and colour) typically reside in open space cavities or pockets of the Core Zone. -Other gem minerals commonly found in these zones include albite, spodumene, tourmaline, and quartz. -Exceptional specimens found in pegmatitic environments are the result of many factors, including extreme crystal fractionation, volatile increases, and long term geologic stability. We'll touch on pegmatites later in a lesson devoted entirely to the gem minerals found in these special rocks. -Fractional crystallization (fractionation) is that process of magmatic differentiation that accompanies the failure of early-forming crystals to react to the melt that remains. The process of fractional crystallization is responsible for the bulk of differentiation that is occurs in igneous rocks.

Chatoyancy

-Chatoyancy is the result of many fine fibre inclusions oriented in a parallel manner producing the well known "cat's eye" effect. This is similar to asterism, thus stones with chatoyancy are also usually cut as cabochons.

Where is beryl found globally

-Beryl is found basically wherever there are pegmatites and pegmatites can be found in most places of the world. So in a very general sense, the potential for gem beryl is very widespread. Unlike emeralds, which require mixing of Be- and Cr-rich rocks, aquamarine can get its chromophore, Fe, from ingredients commonly found with pegmatites. Consequently, aquamarine is the most common of the gem beryl varieties, but typically the "least" valued. -Of course, exceptional specimens of beryl come from only a handful of global locations. Notable are the pegmatites of Colorado, California, and Idaho (USA), the pegmatite fields of Minas Gerais (Brazil), the Ural Mountains (Russia), high alpine pegmatites of Gilgit (Pakistan), and the many deeply weathered eluvial pegmatite fields of Madagascar. All of these localities also produce other gem beryl varieties, such as morganite, goshenite, and heliodor. The geologic environment for emerald formation is much more restricted because the ingredients required (Be + Cr/V) need to be sourced from independant reservoirs. Given this restriction, there are a surprisingly large number of occurrences worldwide but like aquamarines, only a few notable locations stand out. Zambia, Zimbabwe, Madagascar, Afghanistan, Brazil, and Austria all have classical emerald deposits where pegmatite intrudes Cr-bearing schist. The premier locality for emeralds, however, is Colombia. The stones mined in Colombia are by far the nicest stones in the world, achieve good sizes, and have been mined through antiquity.

Why is Beryl Rare?

-Beryl is relatively rare because there is very little of the element beryllium in the upper continental crust and it concentrates only in specific rock types, such as granites and pegmatites -Furthermore, beryllium is not usually concentrated enough to facilitate the growth of larger crystals suitable for the gemstone industry. -Aquamarines are comparably more widespread than emeralds because the chromophore in those gemstones, iron, is found in most geological environments. -For emerald, Cr and V are also required although they are marginally more abundant than Be in the upper continental crust. However, they are concentrated in totally different rock types, such as black shales, peridotites, and basalts of the oceanic crust and upper mantle, requiring unusual geologic and geochemical conditions for the Be and Cr/V reservoirs to meet. -In the "classic emerald model", Be-bearing pegmatites interact with Cr-bearing ultramafic or mafic rocks. However in the Colombian emerald deposits there is no evidence of magmatic activity and it has been demonstrated that circulation processes within the host black shales were sufficient to extract Be, transport it, and form emerald. The more unusual gem beryl varieties, such as red beryl or dark blue beryl, require even more specific geological and geochemical environments and thus are much rarer in nature.

Indicator minerals

-Besides bringing diamond to the surface, kimberlite also entrains non-gem minerals and other rocks formed in the same deep environment. -Sampling such super-deep material allows geoscientists to look at material otherwise inaccessible and to study the inner workings of the Earth. The rocks and minerals that get pulled up are more abundant than diamond, but are not necessarily common minerals on the surface of the Earth. -Minerals that commonly occur in diamond-bearing kimberlites include green olivine, purple pyrope garnet, chromium-bearing diopside, chromium-bearing spinel, and the iron titanium oxide, ilmenite. Detailed descriptions of these minerals can be found in your text. These minerals are often called indicator minerals because of their association with diamond. Their presence on the surface of the Earth can indicate to geoscientists that kimberlite rocks might be nearby.

De Beers change

-By 2006, DeBeers had dropped from 11 major active mines to 7 (South Africa, Tanzania and Botswana), and was competing against 11 other major active mines spread across the globe with significant production volumes and values. DeBeers would later bring the Snap Lake and Victor Projects in Canada to production though neither have been 100% smooth sailing. Despite their reduction in global diamond mining dominance, DeBeers still maintains significant control of the way diamonds are mined, held, distributed, faceted and sold to the end consumer. -Global production in 2007 / 2008 continued to be at very high levels, eventually leveling out in 2010 to ~125 million carats. -The early dominance of Congo/ Zaire/DRC production is clear when considered by carat weight (top), giving way to Australia, Russia, and Botswana. Considered by dollar value (bottom), however, the alluvial production from West Africa is dominant from 1935 to the early '70s, while the lower value of Australia's production greatly reduces its impact. Canada's role starts in the late 1990's and you can see the relative difference between carat produced and value contributed as compared to other countries (such as Australia which shows the opposite trend).

Clarity

-Clarity is a variable that is straight-forward and intuitive. -It describes the internal and external imperfections of a stone. -All diamonds are in some way flawed (imperfect); to be truly "flawless" is extremely rare. -Flaws in a diamond are most commonly solid mineral inclusions, but blemishes can also include fluid-filled inclusions, clouds, feathers, or external features such as scratches, abrasions or burns. -Many of these flaws are inherent in the stone and are present in the rough form as well. -Diamond cutters will often sacrifice carat weight of a diamond by removing included sections of a rough diamond in order to improve clarity. -Clarity rankings range from I (included) to FL (flawless). The GIA has devised a clarity grading system which includes six main categories and further subdivisions. This six-tiered scale is meant to be used by trained gemologists *using only a 10x power magnification loupe* (a gemologist's magnifying lens) - The reason for the specific "10x power magnification" requirement as a standard is that some sort of inclusion will eventually be detected in most (all?) stones if a high enough magnification is used. Thus, for classification purposes, it is only rational that simple tools are used, rather than an expensive laboratory equipment.

What is colour

-Colour is what our brain interprets from the incidence of light (electromagnetic radiation within the visible spectrum) on our eye. In other words, the colour of an object is our eye's interpretation of light in the visible range that has interacted with the object we are looking at -The electromagnetic spectrum is continuous and represents radiation energy ranging from high intensity gamma rays (short wavelength, high frequency) to low intensity radio waves (long wavelength, low frequency). -In the middle of this is the visible region which ranges from about 350 to 750 nanometers (nm). This range comprises the visible rainbow with which we are all familiar with: violet at the short end (~400 nm) and red at the long end (~700 nm). -Light in the visible spectrum (collectively called "white light") is composed of colours (or wavelengths) in the visible portion of the electromagnetic spectrum. -We can use the acronym "ROY G. BIV" to remember the sequence of colours of the visible portion of the spectrum: Red - Orange - Yellow - Green - Blue - Indigo - Violet. - Just outside of the visible region on the shorter wavelength end is the UV (ultraviolet) range and at longer wavelengths is the NIR range (near infrared). -White does not appear as a colour in the spectrum because white light is an even mixture of light of wavelengths across the visible range.

Colour

-Colour of a diamond is one of the more important variables to consumers when choosing a diamond. -Ideally, a diamond is colourless. In reality, almost all diamonds have a yellow undertone and this affects their outward image (Ia). -The colour scale that gemologists use for determining the quality of colour starts from D, which is colourless, and ranges to Z, which is a fairly deeply-coloured yellow and considered undesirable. -When colours are beyond the classification of Z, they are then termed fancy or fancy intense, an indication that their colour is saturated enough to be unusual. This sets these strongly-coloured fancy diamonds into a new category. When a gemologist is grading a diamond they will often have a Master Set of diamonds that span the range from D to Z. The stone being graded is then compared to the Masters and given a classification -Categories D, E, and F are colourless, G to J are near-colourless, K to M have a faint yellow colour, and N to R have very light yellow, and S to Z have obvious light yellow colour. To an untrained eye, the colours D to F (possibly up to I) will appear the same colour, depending on what metal the stone is set in. Stones set in yellow metals may inherit some of the colour from the ring below, while those in white metals will not receive an undertone from the setting.

AGATE

-Common, semiprecious type of chalcedony, agate is the compact, microcrystalline variety of quartz -Most agates form in cavities in ancient lavas or other extrusive igneous rocks -Characterized for the most part by colour bands in a concentric form, and less often by mosslike inclusions (moss agate) -Characteristic bands follow the outline of the cavity in which the mineral was formed (usually) -Band colours are determined by the differing impurities present. -Much of the sliced agate offered on the market in particularly bright colours is dyed or stained to enhance the natural colour which is easy since agate is very porous. -Other names often precede the word agate, and indicate either its visual characteristics or its place of origin -Fortification agate is a type of banded agate with angularly arranged bands that resemble an aerial view of an ancient fortress -Banded agate is produced by a series of processes that take place in cavities in a solidified lava -As the lava cools, steam and other gases form bubbles in the liquid rock that are preserved as the lava hardens, forming cavities. -Long after the rock has solidified, silica-bearing water solutions penetrate into a bubble and coagulate to form a layer of silica gel -This sequence is repeated until the hollow is filled -Some of the layers will have picked up traces of iron or other soluble material to give the bands their distinct colouring -Finally, the whole mass crystallizes, with the water being lost but the band's remaining undisturbed -Moss agate doesn't have banding it is a white or gray with brown, black, or green moss- or tree like (dendritic) inclusions, suggestive of vegetable growth but these are not organic they are inclusions of other minerals, most often iron or manganese oxides or chlorite 15) Onyx -Striped, semiprecious variety of agate with white and black alternating bands -Relatively uncommon in nature, can be produced artificially through dyeing pale, layered agate -Carnelian onyx has white and red bands -Onyx forms from the deposition of silica at low temperatures from silica-rich waters percolating through cracks and fissures in other rocks like other chalcedonies

Coral

-Coral is the skeletal material generated by sea-dwelling coral polyps. For most corals, this material is calcium carbonate, but in the case of black and golden corals, it is a hornlike substance called conchiolin. -Coral has a dull luster when recovered, but can take a bright polish. It is sensitive to even mild acids, and can become dull with extensive wear. -Red and pink precious corals are found in the warm seas around Japan and Malaysia in the Mediterranean, and in African coastal waters. Black coral comes from the West Indies, Australia, and around the Pacific Islands. Coral is used in carvings and beads, and cut as cabochons for use in jewelry. -Coral reefs comprise colonies of marine animals called coral polyps. They form a ridge or hummock in shallow ocean areas. Coral is the most important part of the reef, and generally form its main structural framework. The coral polyps divide again and again, growing into colonies. -A reef becomes limestone by the slow dissolution, redeposition, recrystallization, and chemical transformation of reef material. -Coral is an organic gemstone that is unfortunately associated with a lot of controversy. As you will have read in the "Pearls and Corals" article, coral comes in many different colours, forms beautiful patterns, and can take a high polish. These qualities and its association with the ocean have made coral a very popular material and which, at the same time, have put the coral reefs of the world under significant stress. As a result, a movement to stop the harvesting of coral and introduce synthetic material has been gaining momentum since ~2000. Tiffany & Co Foundation has provided significant funding for these activities, with strong support from a number of international organizations. - Only the skeleton is used as gem material. Determining a coral species through simple observation of a fashioned fragment is a challenge to the gemologist, one familiar to paleontologists. The Corallium genus is by far the most important for jewelry, although a surprisingly wide variety of other corals have been fashioned and often treated. -Main attraction = colour

The Geology of Gem Corundum: Three Main Genetic Models

-Corundum (Al2O3) actually occurs in many rock types. In fact, despite the rarity and value of the rubies and sapphires, corundum itself is not uncommon and is found the world over. The primary factor for its presence is low abundance of silica (SiO2). When both silica and aluminum are present in a growing environment, they will be incorporated into aluminosilicates (minerals containing Al and Si), thereby inhibiting the growth of corundum. -In addition to low Si, an environment with trace amounts of Fe, Cr, and Ti will promote the formation of gem corundum. On top of this, the environment needs to be stable enough over sufficient periods of time to allow growth of crystals that can be fashioned into faceted gems. Based on all the permutations within the proposed overarching source models, scientists believe that the three main sources for gem corundum today are: (1) primary metamorphic corundum in gneisses and marbles; (2) xenocrysts in alkali basalts and lamprophyre; and (3) secondary accumulation in placers

Xenocrystic Gem Corundum in Alkali Basalts and =

-Corundum can also form at great depths below the continents, in the upper mantle. Occasionally, these regions that are favourable for sapphire growth are "tapped" by magmas rising towards the surface. -When these crystals become entrained (or caught up) in another magma, such as an alkali basalt or lamprophyre, they are called xenocrysts (xeno=other, cryst=crystal). -Such corundum xenocrysts have been found around the globe in these host rocks. A few notable occurrences host substantial deposits and quality gems. This deposit model for gem corundum might sound familiar, as it is similar to how diamonds find their way to the surface. -Southeast Asia and Australia each have significant deposits of gem corundum hosted in alkali basalts, although there are also many other global localities. These alkali basalts produce mainly BGY sapphires (i.e., Blue-Green-Yellow sapphires) because significant Fe and Ti are always present in the corundum's growth environment. -Methods of sapphire recovery from these rocks include both primary hard rock mining as well as mining of secondary alluvial deposits formed from weathering on the Earth's surface by streams and rivers. In Australia, occurrences in alkali basalts and secondary deposits stretch discontinuously all the way from southern Tasmania up to northern Queensland. In Southeast Asia, most of the sapphire deposits in Vietnam, Cambodia and Thailand are of alkali basalt origin. -The alkali basalt rocks that host sapphires all share some genetic links. During the rifting apart of continental plates, unusual magmas, including alkali basalts, can be generated below the crust. As the alkali basalt magmas ascend towards the surface they have the ability to entrain material, which can either be xenoliths (rocks) or xenocrysts (crystals). As the magma reaches the surface, the basaltic lavas that extrude will be carrying these xenoliths and xenocrysts. -The xenoliths found in alkali basalts are of the rock type peridotite, which originates from the mantle, and can have associated corundum / sapphire. The presence of these peridotites suggests that the sapphire xenocrysts also originate from the mantle. However, it has been found that not all alkali basalts carry sapphire. Similar to diamond, corundum forming in the mantle is stable only under certain conditions. This corundum window includes only those conditions in which these gemstones can form. This window is broader for corundum than for diamond, and alkali basalts are much more voluminous than kimberlite, making xenocrystic corundum more common than xenocrystic diamond. -Simplified Genetic Model for Alkali Basalt Hosted Corundum. Corundum growth zones occur in association with continental rifting due to an incident mantle plume (hot spot) at the base of the continental crust. As magmas rise from the site of melting, they can entrain corundum during their ascent to the surface, where they erupt as alkali basalts (similar to kimberlite and diamond). Some alkali basalts are corundum-bearing (red triangles) while others may not entrain any corundum (pink triangles), and colours of the corundum are generally quite varied.

Describe the basic relationship between corundum and ruby+sapphire

-Corundum is a mineral few people are familiar with. The mineral corundum also gives rise to different gem varieties: ruby and sapphire. -These two coloured gemstones are the most important of the coloured stones, and account for more than 50% of global non-diamond gem production. -Ruby and sapphire comprise two of the "Big Three" coloured gemstones, with emerald rounding out the group. -Rubies are ubiquitous when describing the purest of reds; the word sapphire invokes images of brilliant blue colours. But sapphires aren't always blue. "Fancy" sapphires are becoming more popular, especially those that are hot pink! In fact, fancy sapphires are actually gem corundum of any colour other than blue or red. -The base mineral corundum, and therefore all its varieties, is in fact a perfect gem mineral. Many would even argue that gem corundum is the most important of all the coloured gemstones. -It is hard (H=9), durable, rare, transparent, and vibrantly coloured with a palette of colours. Corundum has been sourced from many areas in the world over many thousands of years. -Demand for the gem varieties of this mineral has been steadily climbing, making synthetics, imitations, and treated stones commonplace. In fact, nearly 99% of corundum, be it sapphire, fancy sapphires, or ruby, are heat treated to anneal cracks, intensify colours, and improve clarity.

Describe the diagnostic properties of gem corundum (e.g., hardness, refractive index, SG, habit, cleavage, fluorescence)

-Corundum is an aluminum oxide that commonly forms hexagonal barrel-shaped prisms that taper at both ends or as thin tabular hexagonal plates. -It has a hardness of 9 on the Mohs scale, making it one of the most durable commercial gemstones. -It has no dominant cleavage though sometimes has a basal 'parting' and will fracture in a conchoidal manner. -A high specific gravity of ~4.0 (most silicate minerals are ~2.6) results in corundum occurring in secondary placer deposits and recoverable by panning methods, similar to how you would recover placer gold. Refractive index of corundum is ~1.76 to 1.78. -Corundum comes in all colours of the rainbow but is most commonly found as opaque crystals with dull colours. Red corundum is called ruby, blue corundum is called sapphire, and all other colours are called fancy sapphires. -Some varieties of corundum will fluoresce under short wave and long wave UV light if there is enough chromium in the crystal structure but little iron, which tends to quench any emitted energy.

Where is Corundum Found Globally?

-Corundum is found the world over and gem corundum is also found in many global localities. -Heat treatment of corundum has expanded the range from which gem varieties can be sourced since a relatively cloudy non-gemmy stone can be readily transformed into a gem of facet-quality. -The most important historical deposits are those of Sri Lanka, Kashmir, Burma, and more recently, Thailand. Since those early discoveries, there have been great advances in understanding the distribution of gem corundum, particularly due to the realization of its diverse growth environments and the need to fulfill the global demand for gemstones. -Now, the gem mineral is found on every continent, where the most productive regions for gem corundum are historical or currently active plate margins. -In collisional tectonic boundaries, gem corundum can be found in marble-hosted environments. -In extensional tectonic boundaries, they are found in alkali basalts.

How is Corundum Recognized and Distinguished from Other Materials?

-Corundum's hardness of 9 is distinct for this mineral, as is its hexagonal nature. However, both of these properties are more useful in the field than in the jewellery store when it is actually OK to scratch the stone! Because corundum only occurs in specific rock types with specific other minerals, the geological setting can often rule out, or strengthen, the possibility of sapphire or ruby. When cut, important qualities of corundum for identification are its mineral and fluid inclusions, low dispersion, high density, and two refractive indices (it is dichroic). -Sapphires are sometimes confused with spinel, kyanite, benitoite, and tanzanite. Rubies are sometimes confused with garnet, tourmaline, and spinel. All of these stones are further described in your textbook, and we'll learn more about tanzanite, garnet, and tourmaline later in the course.

Chrysoberyl

-Crystals of chrysoberyl aren't uncommon but the gemstone variety, alexandrite is one of the rarest and most expensive gems -Beryllium aluminum oxide -Hard and durable, inferior in hardness only to corundum and diamond, Part of oxides group -Orthorhombic crystal system -Generally occurs in granites or granitic pegmatites, although alexandrites are usually found in mica schists -Since chrysoberyl is so durable, crystals that weather out of the parent rock are often found in streams and gravel beds -Chrysoberyl crystals are commonly twinned -Chrysoberyl can occur in green, greenish-yellow and yellow, to brown colours -Alexandrite is green under daylight and red under tungsten light -Chromium is the colour-producing trace element in alexandrite, replacing some of the aluminum in the structure. -When cut en cabochon, with some parallel, acicular inclusions, chrysoberyl can exhibit the cat's eye effect -Transparent to translucent usually. -Alexandrite is a very valuable Cr-bearing variety of chrysoberyl, normally a light brown or golden colour. It is particularly remarkable as a gemstone because of its colour change properties. Under normal daylight, good quality alexandrite will display a vivid emerald green colour. Under incandescent light (tungsten filament) it will display a strong purple-red colouration. -The reason for this colour colour change is its large absorption band centered in the yellow region (thus allowing greens and some red) as a result of the Cr content and the effect of the different emission spectra of light sources. Daylight emits strongly in the blues and greens in the visible range, while incandescent light is strongest in the red region of the visible range. The end result is the "colour change" effect that alexandrite is famous for. Alexandrite also exhibits strong pleochroism when viewed in constant lighting conditions from different viewing angles. -Stones with strong colour change effects are very rare and rarely reach sizes above 10 carats. Gem specimens with strong colour change can easily fetch up to $10,000 USD per carat, even those of smaller sizes. -The most famous region for alexandrite are the Ural Mountains in Russia. However, good quality stones have also come from Brazil, India, Myanmar, and Tanzania. Although alexandrite has not been discovered in North America, its parent mineral, chrysoberyl has been noted in eastern USA (Maine, New York, Connecticut) and in various pegmatite localities in central and western US, including northeastern Washington State.

What are the 4 C's? (+1 C)

-Cut and polished diamonds are evaluated by four primary variables, all beginning with the letter C (hence the 4 Cs): Cut, Clarity, Colour, and Carat. All variables are equally important and it is their unique combination that defines the value of a diamond. -The standardized 4C system for diamonds was introduced by De Beers in the late 1930's and has gained widespread use across the world by gemological laboratories such as GIA and EGL, as well as jewellers and consumers. Variations on the 4Cs have been used for other gemstones as well, but not to the same extent as with diamonds. -A fifth C has been proposed in recent years to reflect the Country of origin. This has bearing on the historical significance of a stone, but more importantly, on the verification that the diamond is not a conflict stone.

Cyclosilicates

-Cyclosilicates take their name from cycle, meaning circle and are named this because their crystals consist of closed, ringlike circles of tetrahedra the share corners -They are sometimes also referred to as ring silicates -Each tetrahedron shares two of its oxygen atoms with other tetrahedra, and the rings thus formed may have three members (such as benitoite), four members (such as axinite), or six members (such as beryl) -The chemical formulae will each have some multiple of SinO3n where "n" reflects the number of rings

OPAL

-Derives its name from the Roman word opalus -Hardened silica gel, and usually contains 5 to 10 percent of water in submicroscopic pores. -Structure varies from essentially amorphous to partially crystalline. -Precious opal is the least crystalline form of the mineral, consisting of a regular arrangement of tiny, transparent, silica spheres with water in the intervening spaces -Opal is very widespread, in its pure form it's essentially colourless -Vast majority is common or "potch" opal in opaque, dull yellows and reds imparted by iron oxides or black from manganese oxides and organic carbon -In potch opal, where silica spheres are present, they are of many different sizes -Opal is deposited at low temperatures from silica-bearing, circulating waters -It is found as nodules, stalactitic masses, veinlets, and encrustations in most kinds of rocks -It is especially abundant in areas of hot-spring activity and, as the siliceous skeletons of diatoms, radiolarians, and sponges, opal constitutes important parts of many sedimentary accumulations such as diatomaceous earth. -Opal is commonly found as fossilized wood, where it preserves the wood's external appearance and cellular structure -Fossil bones and seashells have been discovered in Australia replaced by precious opal, and it also forms pseudomorphs after gypsum, calcite, feldspars, and other minerals/ -Precious opals can form only in undisturbed space within another rock that is capable of holding a clean solution of silica from which water is slowly removed over a long period. -Silica spheres slowly settle out of solution and arrange themselves into an orderly 3D formation -Unless the spheres are regularly arranged and of the correct size, there is no colour play, which is caused by the diffraction of light through the spheres; opal is, in effect, a diffraction grating -Larger the spheres the greater the range of colour -All precious opal is pretty young since opal can't withstand heat and pressure of burial and metamorphism

Diamond Shapes

-Diamond cuts, or any gemstone cut for that matter, are varied. Certain cuts have been designed to maximize brilliance and fire, while others have been designed to intensify colours -The Round Brilliant is the classic shape seen in most diamonds today. This particular cut was designed based on the physics of light and the physical properties of diamond to return the most amount of light back up through the table of the stone. -Historically, diamond cuts had to be physically undertaken to see the end result. Today, computer modeling software lets us play with how a cut might represent itself on the table or side view of a stone. Multitudes of "designer cuts" have been created but a few notable ones have been well marketed. Examples include "Hearts and Arrows", "Amore", "Arctic Empress" and "Star Cut". The Diaco Inc. website includes 3D animations of the most common cuts and a few other specialty stones (click on 'Shapes' and choose from the drop down list). Round, Marquise (rounded diamond shape with pointed edges, narrow), Emerald/step cut (rectangular with rectange in middle for table), asscher (square with edges cut off octagon as the table), radiant (square with edges cut off but more fire than asscher the table is still faceted smally), princess (square with no edges cut off), pear (tear drop), heart, oval Modelling ray paths of light to emulate a natural setting is a particularly intensive task for computers as there are many many more light sources than we normally think about. Consequently, computer-aided modeling of diamonds has its limitations but can still give us a good idea of what a stone might look like when cut to specific proportions. You may have even noticed the lack of fire, or dispersion in those models seen in Diaco Inc.'s animations. Below are examples of computer generated models of various diamond shapes.

Diamond Testers

-Diamond testers, as the name suggests, are used solely for determining whether a stone is indeed a diamond or another material. -Traditional diamond testers used diamond's superior thermal conductivity to differentiate it from any other stone. Over the years, diamond imitations have become more sophisticated with some having thermal conductivities that come very close to that of diamond. -Consequently, newer tools also test for electrical conductivity. With these two pieces of information, diamond can be distinguished from most non-diamonds. However, synthetic diamonds or treated diamonds will also test positive, as they are the same compound. -More specific tests are needed to distinguish these from natural diamonds, and it is best left to gemological laboratories that are set up with all the tools and toys!

Describe why diamonds are rare

-Diamonds are "rare" because their formational environment is well below the Earth's surface and only special geological conditions allow their transport upwards. However, diamonds are not as rare as most people are led to believe. Their great historical value coupled with a greater geological understanding of their formation since the early 1900's has prompted and facilitated exploration for new sources. -Hundreds of new diamond-bearing pipes have been discovered across the globe although only a handful of those have been rich enough to be developed into mines. -Prior to discoveries in South Africa at the end of the 19th century, diamonds were only sourced from alluvial deposits in India (and briefly from Brazil). There, perhaps only 50,000 carats would be produced annually. In the early 1900's global production was in the millions of carats; by the 1950's it was in the tens of millions. Today nearly 130 million carats of diamond are mined annually. The concept of diamonds as being rare has been perpetuated through history from times when production was scarce.

Describe the geological conditions necessary for diamond formation

-Diamonds are stable only at great depths below the surface, where pressures are very high. -The required depth for diamond growth is at least 150 km (lithosphere --> upper mantle and crust). However, at these depths, underneath large amounts of rock, temperatures are typically on the order of 1500 °C; this temperature is too hot for diamond to grow! -In order for diamond to stabilize, a "cool region" of between 900 and 1200 °C is required. -Consequently, we cannot just pile a bunch of rocks up and expect diamond to form. Instead, we need to pile up a bunch of "cold" rocks so that a locally cool region can exist even at a great depth. -At the center of many continents are collections of rocks called Archean cratons. -These are old (greater than 2.5 billion years), typically cool, and their great thicknesses push a keel down into the upper mantle. - This is similar to how only the tip of a floating iceberg will show above the water's surface. At the base of this keel is an environment favourable for diamond growth, characterized by high pressures and "cool" temperatures, relative to the local environment. -This set of Pressure-Temperature conditions that define the diamond stability field is often referred to as the Diamond Window. - Away from these temperatures and pressures, the stable mineral for pure C is graphite.

Identify the cause(s) of different colours of diamond

-Diamonds can be found in almost all colours of the rainbow, produced naturally or generated through various treatments (usually irradiation) -Natural colour of diamond is primarily related to its classification type, and therefore the type of impurities that are present -Another important variable for generating colour in diamonds is deformation of the crystal, which results in tiny changes in the arrangement of atoms within a crystal (like the actions of bending and buckling but on an atomic scale). -Vacancies in the crystal structure are also important in generating colour and are often tied to the deformation of the crystal lattice -A vacancy is when a hole exists in the crystal lattice where there would normally be an atom -It takes very little of an impurity, cation site vacancy, or crystal defect to generate vivid colours in stones -As a result of subtle differences, not all colours have been fully explained -There are likely multiple explanations for similar colours in diamond -Not all diamonds of a particular brown hue have acquired that hue in exactly the same way

How is Spodumene Valued?

-Kunzite and lower grade hiddenite are fairly common in medium to large stone sizes, and prices per carat range from ~$40 to $100 USD per carat. Of note is a 47 carat stone once belonging to Jacqueline Kennedy Onassis that sold at a Sotheby's auction for $400,000 in 1996. - Of course, the price commanded by this stone reflects its history more than its gemological worth. -Because good hiddenite is much rarer than kunzite, it typically goes to collectors and its price is normally subject to availability rather than a common per carat value.

Can Diamond be Produced Synthetically? How?

-Diamonds have been produced synthetically since the early 20th century -Early experiments were only able to produce small diamonds that were better suited for industrial applications rather than as gemstones -Recently, producers have been able to make gem quality stones Main methods being used to grow gem quality diamonds synthetically: Chemical Vapor Deposition (CVD) and High Pressure High Temperature growth (HPHT) -Diamonds produced using these methods are large enough (around 0.5 carats) to be used as gemstones -Rough sizes of up to 25 carats are being achieved by experimental laboratories and it is nearly impossible to distinguish these from natural diamonds -Companies producing synthetic diamonds (e.g., Gemesis, Element Six, and Apollo) often provide authenticity certificates for their products and inscribe the girdles (the 'waist' of a cut diamond) with identification numbers 1) The HPHT method imitates growth of a natural diamond by creating an environment that is near 1,500 degrees and 60,000 atm of pressure. This pressure is equivalent to loading a 600-km tall column of water on top of a diamond! -Small Seed diamonds are placed in a chamber, which is then flooded with molten carbon and other metal catalysts -The seed diamond crystals act as growing points (i.e, nucleation points) where C atoms attach to as the diamond grows. -The growth process is fairly slow (though fast in geological terms): about 1 carat per day can be achieved -Faceted crystals can be produced up to about ½ carat 2) The CVD method is conducted under low pressure. CVD uses a diamond seed crystal or silicon carbide substrate to act as a nucleating point for the new diamond growth. The key to the CVD method is to flow hydrogen and methane gas (CH4 acts as the carbon source) through a chamber with a plasma flame in the flow path. This effectively destabilizes the methane; carbon is then released and becomes available for attachment to diamond at the nucleating site. Single crystals are grown by this method and after cutting, sizes reach just over ½ carat.

Define and differentiate between primary and secondary diamond deposits

-Diamonds occur in primary and secondary deposits. -Primary deposits are found in volcanic rocks both on the surface and in un-erupted magma that feed volcanoes. -Volcanic rocks that host diamond are called kimberlite and lamproite. -Secondary deposits include diamonds that have been moved from their primary source and concentrated in a new location. -Rivers and nearshore currents are the usual transport mechanisms.

Describe the effects of illumination type on colour

-Different sources of energy will emit electromagnetic radiation at different intensities across the electromagnetic spectrum. -A simple example of this is a light emitting diode (LED) made to emit only one colour (monochromatic). In the case of a red LED, there would only be light emitted with a wavelength in the ~650 nm range and no light emitted anywhere else along the spectrum. -Light sources that are not intended to be monochromatic can have widely different spectral emittance curves depending on the composition of the source of energy we call the "light bulb". -These spectral emittance curves describe the intensity of light at a particular wavelength and will often display data only across the visible spectrum (i.e., ~350 nm to ~750 nm). -The figure below compares the spectral emittance curves (sometimes referred to as spectral distribution curves) of three different sources of light (Tungsten, Fluorescent, Noon), emphasizing the difference in emitted colours across the visible range. -Natural daylight (noon sunlight) is well balanced throughout all colours of the visible light region, incandescent lamps (heated tungsten filament) are skewed towards a warm red, and "Cool White" fluorescent lamps have distinct outputs in specific blue and green regions. -This is why something you buy from a fluorescent-lit store (vegetables, clothes, jewellery) might look a little different when viewed outside in natural daylight or in your home under incandescent light. Businesses that depend on visual appearance to make their sales, such as in retail sales of jewellery, are very much aware of this and usually consult lighting experts to optimize conditions in their salesrooms. -The "Red" LEDs have their maximum peak located near ~650 nm, while "blue" LEDs have their maximum peak located near ~450 nm. "White" LEDs have a more balanced spectral profile than 'coloured' LEDs. Note how all LED emission profiles are not single lines, but a narrow 'bell curve'. From these plots you can see that if you shined a "Red" LED through a non-absorbing transparent solid, like glass, the transmitted light would still be red. Now, if you have a "blue filter" that lets through only 'blue light' and a Red LED is shined at that filter, there would be very little (red) light transmitted through the blue filter. -With respect to gemstones and jewellery, knowledge of how the intensity of light varies according to wavelength is very important when analyzing the resulting colour perceived by our eye. The "colour change" gemstone alexandrite (a variety of the mineral chrysoberyl) is a great example of this. Fine quality specimens will exhibit two distinct colours under specific lighting environments with distinct spectral emittance curves. Other gem varieties that exhibit colour change characteristics include garnet, corundum, and zultanite.

Dioptase

-Dioptase can superficially resemble emerald - sufficiently so that crystals mined from the rich deposit in Kazakhstan were wrongly identified as such when sent to Czar Paul in 1797 -History doesn't record his reaction -Were it not for its softness and good cleavage, dioptase would make a superb gemstone to rival emerald in colour -In prismatic crystals, often with rhombohedral terminations, can be highly transparent, and it is from this that its name is derived: dia, from the Greek for "through," and optazein, meaning "visible," or "to see." -Transparent examples can be weakly pleochroic, and intensely coloured specimens can be translucent -Dioptase also occurs in crystalline and massive aggregates -It forms when copper veins have been altered by oxidation -Superb specimens still come from Kazakhstan, and also from Iran, Namibia, the Congo, Argentina, Chile, and the U.S -Group: silicates - cyclosilicates -Cleavage: perfect -Form/habit: prismatic -Crystal system: hexagonal/trigonal

How is it Recognized and Distinguished from Other Materials?

-Kunzite is easily confused with morganite (beryl), tourmaline, and sometimes topaz, amethyst, and rose quartz due to their colours. -Hiddenite is mostly confused with diopside, beryl, and green glass. -Refractive indices and pleochroic nature can sometimes help differentiate kunzite and hiddenite from other stones.

Primary metamorphic corundum in gneisses and marbles

-Metamorphic corundum deposits provide a significant volume of gem corundum from primary sources. More importantly, it is this primary deposit type that produces the most significant quality of rubies and sapphires. -The metamorphic rocks, gneiss and marble, can host gem corundum mineralization. These rocks can become enriched in Al and depleted in Si under special geological conditions. . -This allows for the aluminum to form a simple oxide (i.e., corundum) instead of an aluminosilicate, a chemical prerequisite for the growth of corundum. -In addition to the appropriate geochemical environment, a high degree of metamorphism is also required, normally up to pressures of ~9 kbar and temperatures of ~750 °C! -Despite the extreme environment required (termed "granulite facies" by geoscientists), corundum is in fact stable over a fairly wide range of high pressures and temperatures, allowing for continued growth during metamorphism of a package of rocks. -The best tectonic environments with these necessary conditions exist predominantly in continent-continent collisional boundaries (such as in northern India, including Pakistan) and sometimes in continent-ocean subduction related zones (such as in the Canadian Rockies). -In the case of marble-hosted corundum, the protolith (the original rock before it was metamorphosed) is limestone which is composed almost entirely of calcium, carbon, and oxygen in the mineral form of calcite (CaCO3), a calcium carbonate. -When this rock is metamorphosed it changes from a sedimentary limestone to its high temperature and pressure equivalent, a metamorphic marble. The calcite in the rock recrystallizes from the sedimentary bioclasts (e.g., fragments of shells or coral reefs) or carbonate mud into new interlocking crystals of metamorphic origin. -But clearly, the marble cannot be entirely pure, otherwise it would lack the aluminum and trace metals necessary for gem corundum to form. A unique environment where these requirements are met is an ocean setting, where limestone typically forms, which is perturbed, and with thin lenses of clay and mud deposits. -It is within these thin lenses of "mud" (which are high in Al and with trace metal content) where mineral reactions take place and gem corundum is allowed to form. Classic examples of localities with marble-hosted corundum are Burma (Mogok and Mong Hsu Stone Tracts), Vietnam (Luc Yen Region), and Pakistan (Hunza). -In the case of gneiss-hosted corundum, the protolith is usually an aluminum-rich sediment. These sediments are similar to the mud that causes the geochemical contrasts within marble, particularly for its aluminum-rich and silica-poor contents. -The geochemistry of these gneiss host rocks is more diverse (i.e., more variety in trace metal content) than that for a marble host rock. Consequently, a larger range of colours is produced for gem corundum in gneiss than in marble. An example of this is Sri Lanka where rubies and sapphires of all colours are found. The same rocks found in Sri Lanka continue into Tanzania and southern Kenya and, as expected, gem corundum of all colours is found in those regions, too.

Can Corundum be Produced Synthetically?

-Due to its simple chemical makeup, corundum has been produced synthetically since 1837 and gem quality synthetic corundum entered the marketplace in the early 1900's. -All colours can be produced synthetically, and very large sizes (more than 100 carats!) can also be achieved using Czochralski's Drawing Method. -This process involves taking the necessary oxide components for gem corundum (e.g., Al2O3, Fe2O3, TiO2, Cr2O3) in powdered form and melting them together in a hot container that is just barely over the crystallizing temperature. A rod with a small corundum seed crystal is lowered into the molten material and then very slowly removed. As the crystal is raised above the nutrient rich molten mixture a small amount of corundum is formed at the interface between the seed crystal and the molten mixture. As the rod is slowly pulled upwards, new corundum continually grows below! -Another common technique for growing synthetic corundum is called the Vernueil Process and involves "dripping" of melted corundum onto bulb shaped corundum crystal. This process is similar to how stalactites form in caves. Luckily, even the best synthetic corundum crystals will show signs of their history by specific identifiable (but often only to trained gemologists) inclusions related to their growth. Synthetic stones, as expected, are considerably cheaper than natural stones.

Morphology of Kimberlite Volcanoes/ Diamond Deposits

-Emplacement of kimberlite volcanoes often results in a vertical and carrot-shaped body known as a diatreme, typically up to 1 km across at the surface. -The figure below shows an idealized schematic of all parts to a kimberlite volcano, however, in most geological settings not each and every part is present. This is either due to variations in the emplacement of the volcano or subsequent erosion on the Earth's surface since eruption. -Root zone = bottom, contains some diamonds -Dykes = narrow bodies near the bottom, originate from the root zone (either like narrow walls in diagram or mini branches from the root) -Crater zone = top, where debris is deposited -Diatreme = the body usually thickest part -Craton = part of the earths crust that has been stable for at least 1 billino years -

Beryl

-Few people have ever heard of the mineral beryl, but everyone has heard of its principal gemstone varieties - emerald and aquamarine, the most common variety -Before 1925, its solitary use was as a gemstone, but since then more important uses has been found for beryllium -Common beryl - a beryllium aluminum silicate - is now widely sought as the ore of this rare element -Other gemstone varieties are heliodor, morganite, and goshenite -Common beryl ranges in color from tan to pale green, pale or sky blue, or yellowish -It is a minor constituent of many granitic rocks and their associated pegmatite dikes, of mica schists, and of gneisses -The name "beryl" is derived from the Greek beryllos, applied to many green stones -Much beryl production is a byproduct of the mining of feldspar and mica, and no large deposits have been found -However, beryl crystals, which normally occur as columnar, hexagonal prisms, are found from time to time: a 220-ton crystal was found in Brazil, and a crystal 19 ft (5.8 m) long and 5 ft (1.5 m) in diameter was discovered in South dakota -Beryl is a cyclosilicates -Form/habit = prismatic -Transparent to translucent -Hexagonal crystal system -Be3Al2Si6O18 = composition

Stages of Fossilization:

-Fossilization is a hit-or-miss process, since normally the body of a dead creature decays, leaving no trace -Main factor is whether or not the plant or animal dies in a location where fossilization can take place. -On a sea bed, where sediments are accumulating rapidly, the chances are good; in an environment where there is little or no sediment accumulation before the plant or animal completely decomposes, the chances are poor -The fossil record is highly biased towards marine organisms with hard parts, such as shells -Where fossilization does occur, it goes through the same stages each time, but how long it takes can vary greatly 1) Silt accumulation → A dead animal's body must be rapidly covered by silt. If it remains exposed, it will disintegrate on the surface 2) Mineralization → Enveloped by sediment, the soft tissue dissolves but minerals are absorbed by the pores of the skeleton 3) Consolidation → The pressure of successive layers of silt hardens both fossilized skeleton and the surrounding silt into rock 4) Exposure → Massive land upheaval lifts the rock layer to the surface. Wind and rain reveal the fossil

Absorbance Graph

-From these two graphs it can be seen that subtractive colour theory can help understand the generation and perception of colour in gemstones. However, it also shows that looking at regions in the electromagnetic spectrum where light is transmitted (ie, not absorbed) can be equally or even more intuitive for investigating gemstones. In these two cases, it is pretty easily seen that transmittance of the blue and red will generate the purple colouration for the sapphire and that transmittance of the green (and a tad bit of red) will generate the warm green in the emerald. You also may have noticed some irregularities in these absorbance plots - for the scientist and gemologist these irregularities (such as the bumps at ~620 nm and ~680 nm in the emerald sample) can help identify the origin and identity of a particular gemstone! -ABSORBANCE GRAPH: Strong absorbance in the green-yellow region leads to a purple hue in this synthetic sapphire.

Why is it Rare?

-Gem bearing pegmatites are rare for a number of compounding reasons. Firstly, these require a geological environment with relatively abundant granitic rocks and where magmas have a chance to evolve and fractionate to the point where a rare-element enriched body is generated. -Furthermore, the material from which the parent magmas are produced also needs to be fertile for rare element enrichment. Ideally, this magma is released from the parent granite and emplaced in sufficiently wide enough dykes that encourage pocket growth. -High volatile concentrations are necessary to facilitate growth of crystals, but not too high that a corrosive environment that would destroy many crystals is created. -For gem minerals to be preserved, pegmatites need to be in a tectonic environment that will allow them to be brought upwards into the crust while not allowing the rocks they are hosted in to deform too much, otherwise crystals may become cracked or broken. -And finally, the slow and steady work of erosion is required to remove enough overlying rock that pegmatites can be found on the surface, either in secondary alluvial deposits or from primary sources.

Identify common diamond treatments (older)

-Gemstones have been treated since antiquity in order to improve their shine, polish, aesthetics, colour and ultimately their value -The world of diamond treatments and imitations is vast and many diamonds are treated to improve their clarity and/or modify their colour. -Because of the high quality of new diamond treatments it is a continual struggle for gemologists to keep up with new techniques and the fingerprints they leave -Diamond-specific treatments are believed to have originated in India before the 2nd century BCE. -These treatments were simple and likely consisted of coatings and dyes, applied directly to the surface of the stone in order to neutralize and undesirable body colour like yellow or brown, or enhance a desirable one like blue. -Archaeological evidence also indicates the use of foil backings in Roman rings to give the stone an apparent colour -Modern diamond treatment techniques didn't take off until the 1950's. Most famous treated-colour diamond in the world: The Deepdene diamond (irradiated and heated in 1955 to intensify yellow hue

Grading Reports, Parts of it

-Grading reports are produced by a long list of gemological institutes and laboratories worldwide that grade stones and jewellery for assessment purposes. -One of the larger institutes is California-based Gemological Institute of America, which has established offices around the globe 1. What is the highest possible grade a diamond could receive on the 3 characteristics described here by a scale? D, Flawless, Excellent 2. Which of the 4 C's is not judged on a scale and why is that so? Carat, -because stones of big and bigger sizes become progressively more rare, value is clearly not linearly related with size -Carat is a specifically weighed out measurement 3. Judging by the report of the specific diamond graded, do you think this is a high quality or low quality diamond, or somewhere in between, and why? I think it is in between a high quality and low quality diamond since it has an excellent cut and virtually colourless, but has very slightly included clarity. In the grading report shown above, note how the main physical properties of the graded diamond are clustered together in sets, and how each diamond graded by the GIA receives a certificate number. This certificate number is engraved on the girdle of each diamond for identification purposes. The number is too small to be seen with the naked eye, but a 10X loupe will allow you to read the number to verify its identity. -Has a drawn out diamond with the inclusions or blemishes labelled on it -Also shows proportions of diamonds on a diagram -Gives measurements and laser inscription registry, -Shows shape, also rates the finish (polish, symmetry) -Also states if there is fluoresence

What are its Imitations?

-Imitation sapphires and rubies have always been around, often times by accident. -Prior to robust testing and mineralogical identification, many spinels and garnets were actually thought to be rubies (similar hardness for spinels). -Mistaken identifications have also been made with sapphires, the most common being kyanite, blue glass, and topaz. As expert identification became more commonplace and prominent in the 1800's, these "misidentified" stones migrated to the "imitation" category when being sold as rubies or sapphires. Today, most of these stones are considered gem varieties in their own right. -Today, imitations for sapphires and rubies are mostly in the form of doublets where natural colourless sapphire/corundum has a coloured synthetic corundum crystal glued underneath. Other composite constructions also exist and can be difficult to identify even with the proper gemological tools.

Compare the composition, crystal structure, and bonding of graphite and diamond

-Graphite like diamond, is also a material composed entirely of carbon. -Graphite has significantly different crystal structure and therefore significantly different physical properties -This phenomenon of a material being of the same composition but having a different crystal structure is known as polymorphism and both diamond and graphite are polymorphs with the composition C -Carbon atoms within graphite are partially covalently bonded, but strong bonds only exist in 2-dimensional sheets. -Bonding between these sheets (ie, perpendicular to these planes) is of the Van der Waals type and are very weak. -Graphite therefore cleaves parallel to these sheets along the (001) plane. Comparing the crystal structures of diamond and graphite using the linked 3D models below, you'll notice that in diamond the C atoms are strongly bonded to each other in 3-dimensions -Each carbon atom is bonded to 4 other carbon atoms forming a tetrahedron. -When you rotate the crystal structure of graphite, the C-atoms are only strongly bonded to each other in 2-dimensions forming infinitely linked hexagons. -Each carbon atom is bonded to 3 other carbon atoms. -Between these planes, Van der Waals bonding occurs.

Briefly summarize the change in diamond production by country through history (First half)

-Historically, India was the sole source of diamonds, however, all of these were mined from secondary deposits and production is thought to only equate to ~10 million carats over its ~4,000 year history. Although this quantity pales in comparison to today's annual global production of around 125 million carats, it is extremely significant because of its historical importance prior to the 18th century and the number of larger diamonds produced (e.g., the Koh-I-Noor). -India and Brazil (alluvial) --> Kimberlite in S.A by De Beers --> Russia non de-beers mine --> australian argyle mine from lamproite (non de-beers) --> Canada 1998 (Diavik and Ekati, non de-beers) -During the exploration of the "New World" by early Portuguese explorers diamonds were discovered in the Minas Gerais region of Brazil. This new source impacted the global industry but was soon eclipsed by the sweeping changes that came with the diamond discoveries in South Africa during the late 19th century. -*This discovery of diamonds within their primary geological source rock (i.e., kimberlite) in South Africa, instead of only in secondary alluvial (river) deposits, changed the industry and many believe this shift is the transition to the "modern diamond mining industry". As the volume of newly mined diamonds increased new markets for diamond consumption were also developed and no longer were diamonds held only for royalty and the wealthy.* -In fact, diamond production from South Africa reached ~1 million carats by 1872, only 6 years after the first diamond pebble was found on the banks of the Orange River near Hopetown by a farmer (Erasmus Jacobs). This region would eventually become known as the Big Hole, or Kimberley Mine, which was taken over by De Beers Consolidated Mines in 1873. -By the early 1900's production in South Africa had increased to ~5 million carats annually from 8 mines and as new mines gradually opened on the African continent annual production was driven to ~15 million carats by 1950. These significant mines include the Premier (opened in 1903, South Africa), Mwadui (1942, Tanzania) and Mbuji Maye (1924, DRC). Later, the countries of Botswana (e.g., Orapa Mine), Namibia (e.g., alluvial and beach deposits) and Angola (e.g., Catoca Mine) eventually opened additional diamond mines and continental production has only increased -Numerous other African diamond-producing countries exist, however, only those mines on primary kimberlite have any significant production.

Summarize the historical sources of diamond prior to 1867

-Historically, diamonds were extremely rare and sourced from only a few scattered alluvial (i.e., within river gravels) localities. They were *first discovered in the Golconda Region of India* and then *subsequently in Brazil* by the 18th century. It has been supposed that a maximum 50,000 carats could have been produced annually from India before the 18th century and that the alluvial sources from Brazil did not produce large amounts. -The word diamond originates from the Greek word adamao, translating roughly to "I tame" or "I subdue". -common name of this mineral is rooted from Greek, it was actually in India where the first appreciation and mining of diamond occurred. -In ancient India, diamonds of euhedral shape (e.g., octahedrons) were the most valued. But the fire (its dispersion of light) and brilliance of diamonds was also recognized as a valuable feature. -One of the most reliable historical pieces of evidence of diamond's value during Roman times comes from the discovery of a rough diamond set in gold within the tomb of a wealthy young woman. To a lesser extent, diamond carving tools also began to be noted in Chinese literature around this time. -European history of diamonds as gemstones can be traced back as far as the 13th century where these stones started to adorn royal jewellery as symbols of power. -or several hundred years the right to wear diamonds was reserved for royalty, and it wasn't until the 17th century that non-royalty individuals started to adorn their own jewelry with diamonds. (still upper-upper class and used for power) -shift in jewellery design also occurred during this time period where diamonds (and other gemstones) became the centers of attention instead of the piece of art that they were hosted within. -diamond cutting became more important and the existing rose and table cuts were replaced with the newly developed old cut. The old cut was essentially the predecessor to the brilliant cut

Metamorphic

-Historically, gem beryl occurrences have been dominantly ascribed to igneous-related sources because it is easy to recognize where and how beryllium enrichment occurs in these environments. However, the discovery and subsequent investigation of what were then termed as "anomalous" beryl occurrences has proven that beryl can form from Be-enriched rocks undergoing regional metamorphism -Furthermore, Be can also be mobilized from these sources and concentrated to the point where an occurrence is economic to mine. Overall controls for metamorphic beryl follow similar guidelines (i.e., source-transport-deposition) as magmatic occurrences. -Like the magmatic model, metamorphic beryl may or may not be associated with quartz veins and hydrothermal fluids. -In the metamorphic-hydrothermal sub-model, hydrothermal fluids dominantly surround those deposits where beryllium is sourced, transported, and deposited as beryl. -Beryl deposits have also been found with no associated quartz veins. In this metamorphic sub-model, the in situ mineralogical transformation was solely due to metamorphism (high pressure and temperature). -The most famous and valuable of all emeralds were deposited following the metamorphic-hydrothermal model. -The emerald deposits of Colombia formed from the interaction of Be-rich hydrothermal fluids with Cr-bearing host rocks during large scale tectonic activity at a convergent margin boundary. This process is similar to the magmatic-hydrothermal setting discussed in the previous section, except that the hydrothermal fluids did not originate from a hot magmatic source but rather were a sedimentary brine forced out from their host rock. Consequently, this sets the Colombian emeralds apart from other emeralds not only for their superior quality, but also for such an unusual geologic environment. A few other settings in the world (Uinta Mountains in USA, Mackenzie Mountains in Canada, Fianel Region in Germany) have given rise to a similar scenario, but none have produced the number, quality, and size of the stones found in Colombia. -Other examples of gem beryl formation in metamorphic environments are the schist-hosted emeralds of Swat Valley (Pakistan) and Habachtal Region (Austria). In these locations, Be-enriched host rock is juxtaposed next to Cr-rich rock through tectonic faulting and shearing. As the two different reservoirs grind past one another, their components are selectively released and able to chemically mix allowing the formation of new Cr-bearing beryl (i.e., emerald). Sometimes quartz veins with beryl can be generated from this tectonic activity as well.

Immersion Cells and RI Liquids

-Immersion cells or vessels, are designed for determining the refractive index of a gemstone. -They can also be used to inspect a gemstone for diffusion treatments, and can quickly show if the stone at hand is a doublet or triplet (a composite stone). -When a stone is immersed in a liquid of the same refractive index, any light that strikes the gemstone will not refract and passes directly through. This allows for any colour zoning in the stone to not be refracted and spread across the table facet (as you would see in natural light). -The resulting image will clearly show whether or not the stone has an even colour saturation, natural colour zoning, or artificial colouration. -In the case of a stone with an unknown identity, the gemologist can check its refractive index by using a set of fluids with known refractive indices. -The gemstone in question is immersed in a series of liquids with increasing refractive indices until no refraction occurs. When this happens, the refractive index of the liquid is equal to that of the unknown gemstone. This establishes one more piece of information to help identify the unknown stone. -Refractive index fluid sets often have increments of 0.005 and range from ~1.4 to ~2.0 (remember that diamond has a very high RI of ~2.418). More sophisticated systems allow the gemologist to control the refractive index of the fluid instead of placing the stone in subsequent drops of different fluids.

Diamond in Canada

-In 1980's, serious discoveries of diamond bearing kimberlite was discovered. -First pipe = in the NWT by ekati mine -In canada there are 3 mines in NWT and 1 in Ontario -Today (by 2012 numbers) Canada is the world's ~3rd top producer of diamonds by value (not by volume though, by volume its 4th) (representing around 12 percent of global production), with four operating mines -The rise of Canada as a diamond producing country has had a major impact on the global industry. 1) In 1991 the *first economic diamond-bearing kimberlite pipe was discovered in the Lac de Gras area in the Northwest Territories* -This became established in 1998 as the Ekati Mine, started by BHP Billiton and now owned by Dominion Diamond Corporation. -It took just under one year for Ekati to produce its 1 millionth carat and now produces between 3 to 5 million carats annually from a number of distinct kimberlite pipes 2) 30 km to the SE from Ekati is the Diavik Diamond Mine in NWT, which officially opened its doors in 2003 and produces approximately 8 million carats annually through a partnership between Harry Winston Corp and Rio Tinto 3) Canada's third economic deposit is De Beers' Snap Lake Mine, also located in the NWT -Discovered in 1997 and started production underground in July 2008 with an expected 1.5 million carats to be produced annually -By December 2015, production of diamonds from Snap Lake Mine halted due to failing diamond prices and increased costs of production 4) Fourth diamond mine, Victor Mine is also owned by De Beers and is located in northern Ontario within the Attawapiskat kimberlite field -It also began production in early 2008 and produces around 600,000 carats annually 5) Gacho Kue in NWT, a joint venture between De Beers and Mountain Province Canada officially opened in September 2016 with an expected annual production of ~4.5 million carats. -Many other sites are still in exploration and development stages or teeter on the verge of becoming profitable mines -Distribution of clusters of diamond-bearing kimberlite in Canada in areas that are underlain by the Canadian Shield -Note how the majority of the known kimberlite localities are hosted in Archean Rocks older than 2.5 billion years. -Because the Archean craton stretches across Canada from northeastern B.C. all the way across to Nunavut and Quebec, the prospective area for diamond mineralization in kimberlite host rock is very high. Indeed, a number of advanced exploration projects and feasibility studies are underway by many different companies. -Old craton is also present in the US and Greenland and some discoveries have been made but none are yet of the scale that Canadian occurrences have shown to be -Archaen craton mostly in Ontario, Quebec, some of Manitoba, and NWT -No diamond bearing kimberlite known in Yukon or labrador, one known in bc (very very eastern side)

Lamprophyre

-In Montana, USA are occurrences of sapphire xenocrysts hosted in lamprophyres. The generally accepted geological model for corundum in these rocks is that the gems formed in the upper mantle (at about 30 km depth) and then were transported to the surface within the intrusive lamprophyre, similar to the alkali basalts and diamonds within kimberlite magma. -The main sapphire deposit in Montana is at a locality called Yogo Gulch. It was first discovered in the late 1800's by prospectors in search of gold and was noted in the bottom of the pans because of its high specific gravity. Over the turn of the century the deposit was worked by artisanal methods of the era, slowing down in the late 1920's and producing only very small amounts today. Over time, a number of other sapphire occurrences were discovered in Montana but Yogo remained the most developed. The host rock for Yogo Gulch sapphires is a young lamprophyre dyke of Eocene age and stretches for approximately 8 km but is only 2 m wide. -Sapphire from Yogo Gulch is historically known as having particularly high quality cornflower blue colour. Crystals rarely contain solid inclusions or colour zoning. This makes them immediately ready for transformation into gems without needing heat treatment. Yogo sapphires form interesting crystals that are typically quite flat and stout as compared to most corundum. Their crystal morphology is very interesting from a gemological and geological point of view, but unfortunately limits the final size of a cut gem. Also of interest is Scotland's Loch Roag where an intrusive dyke similar to the one at Yogo Gulch carries blue corundum xenocrysts.

5) Grossular

-In reference to its gooseberry-green colour, the calcium aluminum silicate grossular is named for the Latin grossularia, "gooseberry". -Predominantly dodecahedral crystals -Can also be white, colourless, pink, cream, orange, red, honey, brown, or black -Crystals up to 5 inch are known -When reddish-brown, it is called hessonite -Ordinarily found in both regional and thermal calcium-rich metamorphic rocks, and occasionally in meteorites -Massive greenish grossular is sometimes marketed under the name South African or Transvaal, jade -Most grossular is opaque to translucent, but transparent, pale to emerald-green faceting material comes from Kenya and Tanzania

Define the main variables used to value gem beryl

-In the gemological realm, all common non-emerald gem beryl is considered to be a Type I gem, as defined by the Gemological Institute of America (GIA). -The GIA defines Type I gems as being essentially free of inclusions and are therefore "eye-clean". -Emeralds are classified as Type III gems, indicating that inclusions within cut stones are common and typically visible by the unaided eye. -Non-emerald beryl of the finest quality can reach up to ~1500 $CDN per carat (1 gram = 5 carats), with the exception of red beryl, which is much more rare and therefore much more expensive. -As a Type III gem, emerald is rarely clean from inclusions. In fact, the characteristic inclusions found within emerald are sometimes affectionately called "le jardin", which is French for 'garden'. -Valuation of emerald is primarily related to the intensity and saturation of colour it exhibits. =Emeralds from Colombia, South America, often display brilliant, almost fluorescent green colours and demand a hefty price -Not surprisingly, simply establishing the Colombian origin of a stone will result in a premium being applied to the piece. -Emerald is one of the most valuable gemstones on a per carat basis and the finest emeralds are rarer than the finest diamonds. -However, due to the relatively unregulated nature of emerald mining and production (as compared to diamond), the value of emerald is much more volatile. For exceptional stones above 10 carats, it is not uncommon for valuation to be in excess of $10,000 USD per carat. -For good stones typical of decent jewellery stores (i.e., up to 2 carats and of good quality), prices are commonly in the $1,000 USD per carat range. -Of course, prices do fluctuate greatly depending on the specifics of cut, clarity, hue, colour, brilliance, polish, origin, and treatment for a given stone. In 2000, one of the highest prices ever paid for an emerald was $1,149,850 for an exceptional 10.11 ct Colombian stone. A recent sale from a Christie's auction for a ring described as "...set with a cut-cornered square-shaped emerald weighing 8.81 carats, with baguette-cut diamond shoulders, and mounted in platinum" fetched $619,000 USD. Sotheby's reports that a sale of a 47 carat square step cut emerald set in a platinum antique necklace sold for approximately $2,600,000 USD alongside a step cut 10.22 carat emerald and platinum ring that sold for ~$600,000 USD.

What are Common Treatments for Topaz?

-Irradiation, heating, and coating are the most common treatments applied to topaz. -Irradiation techniques will generally produce blue topaz from colourless material and intensify lightly coloured blue, yellow, and orange topaz. -Variations in the type of radioactive source, and therefore energy level, for the irradiation process results in a range of colour saturation. -Topaz can be heat treated to generate pink colouration in certain samples. -Topaz is commonly coated by a thin film to produce a variety of optical effects. The composition and thickness of the film will define the change in optical properties, such as uneven modification of colours to produce a play of colours (e.g., Mystic Topaz). -Some coated topaz is susceptible to scratching or chemical attack from household cleaners and is therefore less durable/stable than irradiated or heat treated topaz.

Discuss the significance of the discovery of diamonds in South Africa in 1867

-It wasn't until the discovery of diamond bearing kimberlite at Kimberley, South Africa in 1867 and its subsequent exploitation, that diamonds more commonly came into the hands of not only royalty but also the upper class - Eventually, enough diamondiferous kimberlite pipes were discovered and mined that the middle class was also able to obtain diamonds. Originally, the discoveries in South Africa were made by individuals and mineral claims were hotly fought over. The establishment of the De Beers Consolidated Mines Ltd. in 1888 changed all these, and eventually the face of diamond mining in South Africa.

Lamproite

-Lamproite is another rock type (similar to kimberlite) that hosts diamond, but much less commonly. An important difference between these rock types is in their geochemistry. -Lamproite commonly includes the mineral leucite while kimberlite does not. -In addition, lamproites can exist in areas outside of Archean cratons, unlike most kimberlites. -Only one mine, the Argyle Diamond Mine in northern Australia, produces diamonds from lamproite rocks on a commercial scale. -Notably, the Argyle Mine also produces over 90% of the world's pink diamonds as well as many champagne diamonds!

Describe the behaviour of light (electromagnetic radiation) as a wave

-Light is electromagnetic radiation or energy, and can be described as behaving like both waves and particles (photon). -Like all waves, light can be described by its wavelength, the distance from peak to peak or trough to trough, and its frequency, the number of wave crests (or troughs) that pass through one point in one second. Light propagates in the direction of its wave front. -All electromagnetic radiation (from radio waves to X-rays) travels at a constant speed (the speed of light). -So, when the frequency of light is decreased, its wavelength must increase - this is an inverse relationship. -Light energy increases with increasing frequency (or decreasing wavelength). Refer to the figure and table below for more information on the parts of a wave. -Light also behaves like a particle when it travels as photon particles. More intense light would be composed of a greater number of photons with a higher frequency of incidence. For gemstones, interaction with light is best described using the wave-like approach. For those students interested in the wave-particle duality of light, a good online starting point is Wikipedia.

What are Beryl's Imitations?

-Like with synthetic stones, aquamarine is not typically imitated because it is abundant enough and does not have a high enough demand to warrant imitations. Emeralds, however, have always been subject to imitation. Perhaps the most common deceit is simply green glass, or thin wafers of real emerald glued with green glass or colourless beryl. Other minerals are sometimes marketed as emerald, such as peridot or green diopside, but investigation of the stone's physical properties will always reveal its true identity.

Lazurite

-Main component of lapis lazuli and accounts for the stone's intense blue colour, although lapis lazuli also contains pyrite and calcite and usually some sodalite and hauyne too. -Lazurite itself, is a sodium calcium aluminosilicate sulfate and forms distinct crystals, but is not the same as phosphate lazulite. In lapis lazuli, lazurite is well dispersed. -Best quality lapis lazuli is intense dark blue, with minor patches of white calcite and brassy yellow pyrite. Relatively rare and commonly forms in crystalline limestones as a product of contact metamorphism. Mines in Afghanistan are a major source. -mineral

2) Spessartine

-Manganese aluminum silicate garnet -Crystals are dodecahedral or trapezohedral, and its colours can be pale yellow when nearly pure, to orange or deep red -Pure spessartine is very rare, it is almost always mixed with some amount of almandine, giving the orange to red colouration -Pure spessartine is ordinarily found in manganese-rich metamorphic rocks, and in granites and pegmatite veins -Gem-quality spessartine is rare, and stones are cut more for collectors than for use in jewelry.

Cabochon and Carved Opaque to Translucent Gems

-Many of the gemstones that are fashioned into cabochons or carved do not readily form transparent crystals appropriate for faceting. -However, they typically show vibrant colours or interesting textures that have been valued both in antiquity (e.g., lapis lazuli) and today (e.g., jade). -Within this category of gems, we'll read about lapis lazuli, 'jades', and turquoise although many other minerals can be fashioned in this way.

Microscope

-Microscopes are tools for magnification that are stationary and usually occupy desk-space. They are calibrated instruments with higher power magnification than a hand lens. -They will usually have variable magnification lenses (usually from 10X to 100X) and include a focusing knob to allow investigation of different parts within a gem or mineral. -Microscopes are typically binocular (have two eye pieces) and gemological microscopes will often have a variety of lighting types, including diffuse lighting and spot lighting, as well as a variety of lighting sources e.g., incandescent and full spectrum. -Compared to the human eye, microscopes are much more capable at finding flaws in stones because of its 100X magnification and observations under ideal lighting. =Unfortunately, findings from microscopes are not always representative of how a stone should be graded. We learned earlier that as a rule, the value of a stone is generally based on its appearance to the unaided eye. This is why only a 10X loupe is usually used in grading gemstones. -The microscope is the vehicle into the world of inclusions - the tiny gases, liquids, and solids that exist in every gemstone. Inclusions can take on a variety of shapes and sizes and can create truly beautiful patterns.

List the physical properties, composition, and crystal structure of diamond

-Mineralogically, diamond is pure carbon that is packed into a dense crystalline structure (3.51 g/cm3) with cubic symmetry and perfect octahedral cleavage -Chemical formula = C -Part of the isometric or cubic crystal system, meaning that each of the crystallographic axes is the same length and at 90 degrees to one another (i.e., the unit cell building blocks are simple cubes). -This arrangement has very strong covalently bonded carbon atoms in a highly symmetrical three dimensional network, which makes for an impressively hard, durable, and dense material. -This differentiates diamond from many other minerals in this aspect because ionic bonding is more common than covalent bonding in minerals. -Gemstone/mineral -Ranked at top of the Mohs hardness scale with a value of 10 has high durability, shows a high refractive index of 2.42, and exhibits great dispersion (splitting of light into the spectral colour of a rainbow) -Pure diamond is colourless -Various rare structural defects, elemental substitutions, and laboratory procedures allow diamonds to show the full range of colours found in the rainbow -Very high thermal conductance, low electrical conductance

3) Almandine

-Most common garnet, iron aluminum silicate -Crystals are dodecahedral and trapezohedral and its colour tends to be a pinkier red than other garnets -Rutile needles are sometimes present and when cut en cabochon, shows a four-rayed star -Found world-wide -When it occurs in metamorphic rocks, its presence indicates the grade of metamorphism -Occurs widely in igneous rocks and sometimes found as inclusions in diamonds -Mined for abrasives and cut for gems -Somewhat brittle

Sodalite

-Named for its high sodium content, it is a feldspathoid mineral, a sodium aluminum silicate chloride. Usually forms massive aggregates or disseminated grains. Crystals are relatively rare, and are dodecahedral or octahedral. Principally occurs in silica-poor igneous rocks such as nepheline syenites and their associated pegmatites. Sometimes found in volcanic ejecta and in contact metamorphosed limestones and dolomites.

Rarest coloured diamonds

-Of all the diamond colours, green diamonds and red diamonds are the most rare of all diamond types due to their unique conditions of formation. --Other very rare diamond "colours" include "chameleon diamonds" which change colour upon gentle heating, and are thus termed 'thermochromic'. Although it sounds spectacular, the colour changes are usually very subtle and shift between pale browns, yellows and greens. -Coloured diamonds are generally more expensive than colourless diamonds; however, weakly coloured stones are usually less desirable than perfectly colourless diamonds - There is a bit of subjectivity and marketing skill for pricing intermediate off-colour diamonds. -Strongly coloured diamonds (of which only a dozen or so are found globally per year) on the other hand, can be extremely valuable and command top dollar per carat. -In natural stones, the best reds, blues, and greens can cost on the order of ~$1,000,000 per carat or more depending on the history of a stone.

Shale

-One of the most abundant sedimentary rocks, shale consists of silt- and clay-sized particles deposited by gentle transporting currents, and laid down on deep-ocean floors, basins of shallow seas, and river floodplains -Shales differ from mudstones in that they easily split into thin layers -Most shales occur in widespread sheets up to several yards thick, although they are also found thinly interbedded with layers of sandstone or limestone -Shales consist of a high percentage of clay minerals, substantial amounts of quartz and smaller quantities of feldspars, iron oxides, carbonates, fossils, and organic matter -Reddish and purple shales result from the presence of hematite and goethite; blue, green, and black from ferrous iron; gray or yellowish from calcite -A valuable raw material, shale is used to make tiles, bricks, and pottery -Rock type: marine, freshwater, and glacial detrital sedimentary -Major minerals: clays, quartz, calcite -Gray colour and fine texture -Oil shales are organic-rich shales containing kerogen, a complex mixture of solid hydrocarbons derived from plant and animal matter -In oil shales these are present in high enough quantities to yield oil when subjected by intense heat

Basic Tools - Unaided eye

-Our most important and reliable tool is simply our eye, unaided and unhindered. -It gives us immediate information about the colour of a stone, although that is not always diagnostic. -A trained eye can estimate the dispersion of a stone, observe crystal habits, fractures, and cleavages, and identify characteristic inclusions and associated minerals. -The eye also allows us to collect observations using other methods, and along with the brain facilitates the combined contextual interpretation of all our observations. For a little boost, hand lenses and magnifying glasses are often used to look at the finer details.

Where is Corundum Found Locally?

-Our neighbor to the south has provided the world with stones primarily from Yogo Gulch, as well as a few from the Appalachian Mountains in Maine and a few select regions in Idaho. Although Canada is not yet a commercial producer of corundum, there are a handful of gem localities, a number of significant non-gem occurrences, and vast swaths of prospective ground in our country. -The most developed gem corundum project in Canada is undoubtedly the Beluga Sapphire Occurrence on Baffin Island, Nunavut. This locality is thus far the only source of high quality corundum with good transparency and colour. The marble-hosted geological model explains the presence of corundum in this area. The host rock is a ~2 billion year old metamorphosed limestone (marble). -In 2002, two Inuit prospectors, brothers Seemeega and Nowdluk Agpik, discovered several gem quality blue sapphires just outside the town of Kimmirut. Following their discovery, True North Gems acquired exploration rights and has been continually searching the region for additional corundum. They have conducted bulk sampling and diamond drilling and have uncovered crystals with dimension of up to 8 cm long and 2 cm wide with weights to ~1 kg. -Cut stones from this locality show a variety of good untreated colours, achieving weights up to 1.5 carats. Heat treated stones also show good colours and have been cut up to 7.81 carats. This occurrence has great promise to become a Canadian source of sapphires and even more promising is the fact that the prospective host rocks extend for 100's of km into the high tundra. Watch for news as more discoveries are bound to happen! -Newfoundland and Nova Scotia are home to blue-hued corundum and pink sapphire, respectively. The region in Newfoundland has officially produced a small amount of material, with the largest pieces being a ~22 carat cabochon and a ~2.4 carat step cut stone. Nova Scotia hosts some red corundum with the largest stone weighing 1.3 carats but with significant inclusions. In Ontario, the Bancroft area has produced a spattering of cut gemstones, many of which are fashioned into cabochons to accentuate asterism. These stones are typically black to grey to blue and range up to about 30 carats. Some notable blue sapphires from the York River area weigh up to ~6 carats and are housed in the Canadian Museum of Nature. British Columbia is another source of six-rayed star sapphires with some cabochon-cut stones up to ~12 carats recovered from the Slocan Valley. The colour of these stones is typically blue-grey and some are brown to black. These stones occur in high grade metamorphic rocks. More exciting, however, is a recent discovery of blue to deep pink sapphire hosted in marble in eastern B.C. at a private location. These crystals have been cut into gems of up to ~0.5 carats and some are verging on being classified as red rubies. Watch for news on these two southeastern B.C. finds too! In addition to the two metamorphic-related corundum occurrences in B.C., there are a number of alkali basalt localities with all the right ingredients for corundum. Thus far, no reports of sapphire have been made, however, most people working with these rocks are not usually looking for gemstones.

What is a Pegmatite?

-Pegmatite is the premier rock type for finding large high quality gemstones, and with the exception of diamond, can produce basically the whole range of the most sought after coloured gems. -Not all "pegmatite gems" occur in "all pegmatites" - most are restricted to specific varieties of pegmatites and some even more restricted to the type of host rock these igneous rocks intrude. Further, pegmatite gemstones tend to occur in specific locations within a pegmatite called pockets. -As alluded to, pegmatites supply the world with the best tourmaline, topaz, and beryl along with a large selection of other rare stones - some so rare that their faceted varieties are only cherished by the few collectors who can get their hands on them. In addition to the wonderful gems that pegmatites produce, these rocks are also important hosts for rare metal deposits, including lithium (Li), tantalum (Ta), niobium (Nb), and tin (Sn). -Pegmatites are known for growing the largest crystals and are the environment for many "largest crystal" records for specific minerals. In fact, the term pegmatite is used as a descriptor for igneous rocks with large crystal sizes. -Pegmatites and their mineralogy First, what is a pegmatite? Prof. "Skip" Simmons, a "pegmatologist" from the University of New Orleans, defines these wonderful rocks as intrusive igneous rocks that are texturally very coarse to gigantic in size. -The mineralogy of pegmatites is directly tied to their geochemistry and most pegmatites can be characterized by a base composition similar to granite but with significant enrichment in rare elements. So let's start with pegmatite geochemistry and then work towards the rare minerals that can form from these rare elements. -Rare elements that are commonly enriched in pegmatites include: Be, Li, Cs, Ta, Nb, Y, F, Rb, Sn, Ga, and B. What a list! Dig out your periodic table of elements! The following table gives oxide composition of typical granite, common pegmatite, and gem bearing pegmatite. Note the increase in Li, P, F, B, Be, Rb, and Cs in pegmatites relative to granite. -The enrichment of these unusual elements leads to the formation of unusual minerals. Unless one is a pegmatite mineralogist, many of the minerals that pegmatites host are completely unfamiliar, yet, because of their rarity, they often make it into the gemstone world. The rarest of the unusual pegmatite minerals normally go directly to rare mineral collectors. -An example of one of these rare minerals that you're already familiar with is beryl. This mineral's chemical formula is Be3Al2Si6O18. In regular granite, sourcing the O, Si, and Al would not be a problem. Sourcing the Be is a bit more difficult. However, because Be is a "fairly common" element in pegmatites, beryl is a "fairly common" mineral in these unusual and exciting rocks. The following table lists many of the gemstones found in granitic pegmatites, sorted by abundance. The list contents were summarized by Prof. Simmons. Remember that a gem name might differ from the mineral name, e.g. aquamarine (gem variety of the mineral beryl) and kunzite (gem variety of the mineral spodumene). PEGMATITE = VERY COARSE-GRAINED, IGNEOUS ROCKS, most have QUARTZ AND FELDSPAR.

Pegmatite Morphology

-Pegmatites and their internal morphology are often described by their zonation, which is based on mineral distribution and overall rock structure. -A zone is defined as a region within a pegmatite with a common or regular set of minerals and textures. These zones tend to form concentrically but not necessarily evenly, and earlier zones are subject to modification by later events. -Simple pegmatites have homogeneous textures and simple mineral assemblages throughout the igneous body, showing no segregation into discrete zones. These types of pegmatites tend to have many crystals of smaller size rather than a small number of larger sized crystals. The simple mineralogy (e.g., quartz, feldspars, micas) and small grain size limits their gem potential. -Zoned pegmatites are heterogeneous, differentiated and exciting! They consist of a "core" zone surrounded by distinct zones moving outwards through the core margin, intermediate zone, wall zone and finally the border zone. -These types of pegmatites are often symmetrical in cross section but will show irregular 3D shapes when the pegmatite is considered in full. -Sometimes not all zones are present in a single cross section, but would be present if the pegmatite was looked at as a whole. -Thicknesses of the different zones depend on the individual pegmatite and the pegmatite field and crystal sizes in general coarsen towards the core. -The border zones consist of finer grained crystals comprising feldspars and quartz with the occasional tourmaline or garnet. (granitic) -Wall zones are medium to coarse grained and also consist primarily of feldspars and quartz; minerals such as garnet and beryl start to appear here. -The intermediate zone is where we start to see very coarse crystals and also where significant gemstones begin to appear. In this zone, the mineralogy is dominated by feldspars but the tourmaline variety starts to change from schorl to elbaite. -The core margin is a nucleating site for gem minerals that will eventually grow unhindered into the core zone where pockets exist. Extremely coarse gem quality crystals are common here and typically include beryl, spodumene (kunzite), elbaite, and other rare element minerals. tourmaline, beryl, spodumene -Inwards from the core margin is the core itself, which is most commonly composed of QUARTZ. -However, this is the most common region where pockets develop and where the best crystals grow! These regions are usually fluid-filled close to the end of a pegmatite's life. This environment allows crystals that have started to grow on the core margin to extend as far as they can into this pocket. Truly magnificent specimens from pegmatites usually originate from pockets. Many pegmatologists love to say that you haven't lived until you've unearthed a pocket zone! -Complex pegmatites are zoned pegmatites that have been altered from their original concentrically zoned form by further influx of evolved fluids or magma with high volatile content (e.g., H2O, B, (PO4)-2, F). -Often, this overprint will be of either LCT or NYF geochemical character. Textures in these pegmatites will include all those in the zoned pegmatites, but many minerals are partially or fully destroyed from corrosion, while new mineral assemblages are stabilized. These pegmatites also produce fantastic mineral specimens and they also tend to be the best type for rare metal ore deposits.

Where is it Found and Mined Globally?

-Pegmatites are found across the globe, but high quality gem bearing pegmatites are much rarer. Famous localities include Brazil, Madagascar, Russia, Pakistan, and the United States. Other notable regions include Italy, Mozambique, Namibia, and Afghanistan. -The best gem pegmatites in Brazil, and arguably the world, occur in a region called Minas Gerais. It is located ~500 km north of Rio de Janeiro and consists of a very prolific pegmatite region. The following map is modified from Proctor (1984) and shows the distribution of pegmatites and their primary gem content. -In the United States, the Pala District of California has produced some of the most magnificent rubellite tourmaline, in addition to top quality morganite and aquamarine in the world. Read this article by Mark Mauthner published in Rocks & Minerals, which details the discovery of the "49er Pocket" where hundreds of gem specimens, from good to very fine, have been recovered. Use this Mauthner-2008 Reading Guide to help you with the article. -In Colorado are pegmatites of the Mt. Antero region just southwest of Denver. This area is known for some of the best aquamarine crystals in North America. Bryan Lees, in his 2005 article in Rocks & Minerals, describes the excavation of a gem bearing pocket from this region. The article is optional, but is an interesting read if you are inclined to do so - access it from the Introduction to this Lesson. Another notable location in the U.S. is the Mount Mica mine in Maine. This area has produced beautiful material since the early 1800's

How Big Do Pegmatites Get?

-Pegmatites consistently produce the largest gemstones of any rock type. Beryl crystals over 1 m in length are common and some of the largest specimens have been on the order of 18 m! Large gem quality stones from pegmatites include heliodor (up to 2,000 carats), aquamarine (the "Marta Rocha" weighs ~75 lbs), morganite (the "Rose of Maine" weighed more than 50 lbs when it was first uncovered), tourmaline (Paraíba variety up to ~50 carats), spodumene crystals over 10 m in length, and topaz crystals over 200 lbs.

Olivine

-Peridot is its gemstone variety -Olivine is applied to any mineral belonging to the forsterite-fayalite solid-solution series, in which iron and magnesium substitute freely in the structure -Fayalite (Fe2SiO4) is the iron end member, and forsterite (Mg2SiO4) is the magnesium end member -Most common intermediate olivines have compositions near the forsterite end of the series, and most peridot is about 90 percent forsterite -Olivine group includes the rare mineral liebenbergite and the less rare tephroite Olivine Properties -Crystals are tabular, often with wedge-shaped terminations -Can also be massive or granular -Forsterite-fayalite olivines are usually yellowish-green but can be yellow, brown, or gray -A result of the small amounts of iron that are almost invariably present cause its colour to vary from white for pure forsterite to black for fayalite, but both are very unusual. Olivine in the crust -Olivine is inferred to be a major component of Earth's upper mantle and probably one of the most abundant mineral constituents of the planet -Olivine has also been found in some lunar rocks and in stony and stony-iron meteorites -Generally the first mineral to crystallize from rocks with relatively low silica content; thus, its composition reflects to some extent that of its parent magma -Thick accumulations can occur as a result of olivine crystals settling through a body of magma that is still partially magnetic -Olivine occurs most commonly in mafic and ultramafic igneous rocks such as basalt and peridotite -The forsterite (magnesium-rich) end of the olivine series forms in low- and very low- silica environments like metamorphosed limestones and dolomite, while the fayalite (iron-rich) olivines form in more silica rich conditions -In the presence of water at low temperatures, olivine readily undergoes hydrothermal alteration, forming serpentine, talc, chlorite, or magnetite -Common olivine has a high melting point, and is used in the manufacture of heat-resistant bricks

Iridescence or Opalescence

-Play of colour from internal scattering of light off of fine particles in a mineral is known as iridescence or opalescence, but is sometimes described as "schiller". It is commonly seen in the gems sunstone and opal.

Polariscopes

-Polariscopes are essentially sophisticated benchtop dichroscopes in which a more controlled environment is created. -This is particularly useful for stones with two or three refractive indices that are very similar (e.g., the quartz family of gems), and therefore will not show pronounced changes in a dichroscope. -Polariscopes are often used in conjunction with immersion cells.

Pseudochromatic minerals

-Pseudochromatic minerals show colours and optical effects through dispersion and scattering of light. Colour and optical effects generated from scattering includes asterism, chatoyancy, iridescence, opalescence, and labradorescence. -Colour generated from dispersion, as we learned earlier, is the result of light passing between media with varying refractive indices. Gemstones with higher values of dispersion will show greater spreading, or dispersion, of colour. Diamond is a well-known example of colour, or "fire", generated through dispersion. The minerals calcite, moissanite, sphalerite and zircon are all great examples as well.

Explain the differences between the different gem corundum varieties (e.g., ruby, sapphire, fancy sapphire, corundum with asterism)

-Pure corundum is colourless and clear if transparent or pale white if opaque. This mineral also has low dispersion so the value of the stones comes not from fire generated (as in diamond), but rather from the intensity of colours seen. -The vivid colours of corundum gem varieties, such as ruby and sapphire, arise primarily from elemental substitution in the Al site by transition metal elements. The most common cations to substitute are Fe+2, Fe+3, Ti+4, Cr+3, and V+3. -A continuum of colour saturation exists between pink sapphire and ruby that is correlated with trace amounts of Cr. There is no official cutoff for the amount of Cr needed for ruby, but usually rubies will have up to ~1 wt% of Cr2O3. When Cr substitutes for Al, wide absorption bands are generated in the violet (~450 nm) and green-yellow (~500 nm) ranges, as well as overlap a bit into the blue region. -The red region of the electromagnetic spectrum (~650 nm) does not have very much absorption at all and results in all colours but red being blocked by ruby. -But there is another trick up ruby's sleeve that makes its red almost jump out at the observer. When Cr is introduced into corundum it makes the mineral fluorescent under UV light. This means that UV energy from normal light is accepted into the crystal and then re-emitted at a lower energy level - conveniently in the red region, thus amplifying the intensity of red in ruby under daylight conditions. -However, if any iron is present it will usually absorb the red fluorescence from UV light. Thus, the finest rubies are those that have little to no iron in their crystal structure. -Blue sapphires are generated primarily from pairs of Fe+2 and Ti+4 substituting into the crystal structure for Al+3. The process of intervalence charge transfer (essentially continual swapping of electrons, bouncing back and forth) occurs between the Fe and Ti and all colours except blue are absorbed. -So like ruby, it is the absorption of all other colours from full spectrum light (aka white light) that generates the beautiful blues in sapphires, rather than the "generation" of the blue colour. Very small amounts of these elements (only ~0.01 wt% Fe and Ti) are needed to produce the vivid blues. -Other colours are generated from a combination of these elements, as well as other minor cations and defects in the crystals. Also, a single corundum gemstone can be multi-coloured from different concentrations of metals in different parts of the crystal - this is called zoning. The figure below is an example of a hypothetical crystal showing oscillatory (back and forth) zoning and a red core. You can see that the zones with Ti and Fe show up blue, those zones with no impurities are colourless, and the core with Cr exhibits red colouration. -Some sapphires also show an optical characteristic called asterism, which is most commonly seen as a six or twelve pointed star. These "arms" of the star are generated from oriented inclusions of long and skinny minerals (almost always the mineral rutile, a titanium oxide, TiO2). Specimens found with these inclusions are often cut and polished in a rounded and polished cabochon style to emphasize the nature of this optical effect. Rutile inclusions can occur in both sapphires and rubies, although it is more common in sapphires.

7) Uvarovite

-Rarest of all the gem garnets -Calcium chromium silicate -Predominantly dodecahedral crystals are always too small to be cut -Colour comes from chromium- same colouring agent that is in ruby and emerald, which is known to have an inhibiting effect on crystal growth -Found in chromium-bearing igneous and metamorphic rocks -Some of the largest crystals come from Outokumpu, Finland

Isotropic medium

-Recall from previous lessons that some minerals belong to the isometric crystal system and others to the monoclinic, triclinic, orthorhombic, tetragonal, and hexagonal crystal systems. -Minerals that belong to the isometric system are also isotropic minerals because they have only ONE refractive index that is applicable in all 3-dimensional orientations. -Examples of isotropic minerals with a single refractive index are diamond (n=2.419) and spinel (n=1.725). -Material from all crystal systems other than isometric show more than one refractive index and are termed anisotropic.

Describe the genesis of pegmatites using the terms parental pluton, fractionation, dykes, fertile or barren magma

-Recall the definition by Prof. Simmons, "pegmatite is a textural term used to describe very coarse to gigantic sized textures in intrusive igneous rocks". -In addition, most pegmatites are genetically associated with larger igneous bodies and will have a base geochemical signature similar to their parental pluton (a pluton is a body of intrusive igneous rock that is crystallized from magma slowly cooling below the surface of the Earth) -The parental pluton, commonly granite, is a key factor in the genesis of most pegmatites in that it gives rise to, or feeds, a pegmatite. -During the magmatic history of a granite body it may undergo significant fractionation. -Fractionation is a process that involves the sequential crystallization of minerals as granitic magma cools. As certain minerals crystallize, they essentially remove the elements required for it from the molten magma. -As the magma cools further, it becomes more depleted in the elements which make up the minerals that have crystallized. -An analogy would be like eating a specific colour of Smarties from a box. If you start eating only the blue ones, there will still be lots of Smarties remaining, just not many blue ones and a larger proportion of the "residual" (non-blue) Smarties. -In a magma, after the elements needed for the first mineral to crystallize are removed, there will still be magma remaining, just not much of the elements needed for the first crystallized mineral and a greater proportion of "residual" elements not used in that first mineral. -What's left is a progressively evolved or fractionated granitic magma that is composed of the "dregs" or "residual" melt (the yellow, red, and green Smarties). What is significant is that rare elements like Be, Li, Ta, and Cs (among others) do not fit nicely into the crystal structures of the earlier crystallized minerals and consequently get strongly concentrated in this "left over" magma. This is the good stuff. -When the conditions are just right, this highly evolved magma with high concentrations of rare elements injects itself into the overlying host rock, forming dykes. These dykes are normally on the order of a few meters but sometimes can be up to ~100 m across or only cm's.(Dike, also called dyke or geological dike, in geology, tabular or sheetlike igneous body that is often oriented vertically or steeply inclined to the bedding of preexisting intruded rocks;) -Magmas that generate these highly fractionated pegmatites are often called fertile while those that are not are called barren. Pegmatites originating from a fertile granite will often show geographic zoning of rare metal enrichment. Typically, the farther from the fertile granite the more fractionated the pegmatite is. -Schematic representation of regional geochemical zoning in pegmatites with an associated fertile parental granite. Note the increasing degree of evolution and geochemical complexity away from the parent pluton and that within the pluton there will be little rare elements remaining, as they have all moved outwards with the pegmatite magmas.

6) Hessonite

-Reddish-brown variety of grossular -Calcium aluminum silicate -Mostly found in dodecahedral crystals, its colour is due to manganese and iron inclusions -Popular name is "cinnamon stone" -Hessonite is found principally in calcareous metamorphosed rocks -Most important source of gem quality hessonite is in the gem gravels or metamorphic rocks of Sri Lanka

Refractometer

-Refractometers are used to determine the refractive index of a faceted stone through refraction and reflection of light. -They are not usually "pocket-sized" tools, but come in compact portable versions as well as desktop versions. -These use the same concepts of light as those by dichroscopes, i.e., the degree to which specific wavelengths of light will bend and slow down depends on the refractive index of the medium. -However, the refractometer differs from dichroscopes in that it does not use transmitted light. -This allows the user to determine the refractive index of translucent to opaque materials like jade, hematite, or turquoise. The information derived from a refractometer reading is objective and quantitative and can be quickly compared to tables. -Consequently, this tool is very useful for difficult or unusual stones and, in combination with the loupe and Chelsea filter, allows the identification of almost all common gemstones.

Hammers and Chopsticks

-Rock hammers are less useful in a gemological setting (just try to bring one into a jewellery store!) but are essential for mineral or rock collecting. -A simple carpenter's hammer will not suffice, it is important that an actual rock hammer is used because these tools are specifically hardened so as to not splinter when struck against a rock. -Estwing is a common brand in the geological rock hammer world and they make a great 22 oz. hammer with a pick on the back end for prying open tough rocks. -Personally, I prefer a Geotul, which is a hammer with a 30" long shaft capped by a 2.5-lbs hardened head that is backed by a flat ended pick. -It breaks most rocks, and for those it can't, there is always the 10-lb sledge that stays in the back seat of the truck. -For cleaning away dirt and debris from mineral specimen in the field, chopsticks and paint brushes are very effective and usually soft enough that they will not damage any delicate crystals.

How is Topaz Recognized and Distinguished from Other Materials?

-Rough topaz is quickly identified by its crystal shape, mineral and rock associations, and hardness. -Tumbled (alluvial) topaz is identified best by its hardness, basal cleavage (perfect), and high density. -Topaz can be easily confused with the multitude of minerals that have inherited its name as a modifier. -Examples are "topaz quartz" (actually citrine) and "smoky topaz" (smoky quartz); topazolite is actually yellow garnet! Topaz with brown to reddish-orange hues can be confused with zircon, and light blue topaz is often mistaken for aquamarine and apatite. Pink topaz is easily confused with tourmaline, kunzite, and spinel.

How is Tourmaline Recognized and Distinguished from Other Materials?

-Rough tourmaline is quickly recognized by its prismatic habit, striations along the crystal's length, pseudo-hexagonal outline (also see images in your textbook), and association with pegmatites and other pegmatite minerals. Beryl also has vertical striations and is also hexagonal, but it is harder, shows true hexagonal outlines, and less commonly forms fan-shaped crystals or clusters. Quartz is also a hard hexagonal crystal but it shows prominent striations across the long axis. -In identifying tourmaline fragments, look for strong dichroism, where the colour (and its saturation) observed down the crystal's long axis is much different than across the long axis. In tourmaline, the more saturated / darker of the two colours tends to be oriented along the length of the crystal (along the c axis) while the lighter colour is oriented across the crystal. -Of course, it will not be possible to tell which way the crystal is oriented when observing a water worn pebble. -In this case, rolling the stone around while using a dichroscope usually makes the colours show. In cut stones, diagnostic properties include strong dichroism, refractive indices of ~1.61 to 1.66 and a SG of around 3.

Amphibolite

-Schistosity and foliation are well developed in most amphibolites -Made up predominantly of amphibole minerals, such as actinolite, many samples contain microscopic grains of feldspar, pyroxene, and calcite -Some also contain macroscopic crystals of minerals such as garnet, diagnostic of regional metamorphic rocks formed under low to moderate temperatures and pressures -Amphibolites form from the metamorphism of mafic igneous rocks such as gabbros, and can also form from sedimentary rocks such as graywacke -Can be used in road-building and other aggregates since it is very strong and durable -Regional metamorphic -Temp and pressure: low to moderate -Structure is foliated and crystalline -Major minerals: hornblende, actinolite -Gray, black, greenish colour -Coarse texture Define the main variables used to value gem beryl Identify common treatments and imitations of gem beryl State if beryl can be produced synthetically

Schist

-Schists are foliated metamorphic rocks with visible mineral crystals -They commonly show distinct layering of light and dark-coloured minerals -Most schists are composed largely of platy minerals such as muscovite, chlorite, talc, biotite, and graphite -Schist's characteristic schistose fabric (it splits easily along planes) is a result of the parallel orientation of these minerals -There are a number of different schists -Greenschist is a schist rich in green minerals chlorite, actinolite, and epidote; blueschist is rich in blue glaucophane -The specific mineral composition of schist depends both on its original rock (protolith) and on its metamorphic environment -The mineral assemblage can thus be used to help determine both the environment in which the original rock formed and its metamorphic history -Rock type: Regional metamorphic -Temperature and Pressure: Low to moderate -Foliated structure, medium texture, silvery, green, blue colour -Major minerals: Quartz, feldspar, mica

Secondary Modifications

-Secondary modifications usually occur during two distinct phases in a diamond's life 1) After growth but during transport to the Earth's surface by kimberlite magmas. Modifications here include corrosion of diamonds along preferential weaknesses that are prone to chemical attack (this is analogous to someone preferentially digging in soft sand instead of on a concrete sidewalk). 2) During transport while on the Earth's surface. Primarily the result of abrasion during river or alluvial transport -Corrosive modifications during transport (or sometimes in an original unstable growth environment) give rise to rounded edges of primary crystal growths (which are usually octahedrons). -The end product is a diamond with strongly rounded features almost approaching the shape of a beach ball -Sometimes there will be multiple growth and corrosion events in a diamond crystal's history, which can lead to highly complex and intricate shapes -Modifications during transport of diamonds in alluvial settings are minor when compared to modifications during magmatic transport -The most common alterations result from processes on the Earth's surface (mainly mechanical abrasion) and are manifested as scratched surfaces on the diamond or as abraded crystal edges -Because of the good durability and high hardness of diamonds, it can take many millions of years to significantly abrade a diamond from processes on the Earth's surface -Often, a particular diamond bearing pipe or sets of similar pipes will show similar diamond morphologies - this has been used in some cases to try and tack the origin of "unknown" diamonds back to their source

Summarize how the dominance of the De Beers group has changed in the last century

-Shortly after the turn of the 20th century, the diamond industry consisted primarily of the De Beers group who were mining the large majority of diamonds from South Africa and also marketing them to the consumer. Having a single organization controlling the majority of diamond production and sales has had a profound impact on the development and evolution of the global diamond industry -The subsequent rise of competing diamond producers (Soviet Union in the 1950's, Australia in the 1980's and Canada in the 1990's) and the drive by consumers to ensure conflict-free diamonds has significantly changed the way diamonds are mined, polished, and sold. -Today, the global diamond industry has a handful of major corporate players, which means that De Beers' production contribution is now down to about 35% of the global total by value (as of ~2014). A number of government and non-government organizations now regulate the movement of diamonds, a highly valued commodity with significant liquidity, and are working to ensure the civil rights of miners. The Kimberley Process monitors the import/export activity of participating countries, keeping tabs on legitimately mined and processed diamonds. -today Debeers % 60

What Colours can Tourmaline Have? How are These Colours Generated? What Gem Varieties Result?

-Similar to beryl, the colour in tourmaline is most commonly caused by transition elements substituting into the crystal structure for Al. -In elbaite, the most common gem quality variety of tourmaline, the common substitutions that produce different gem varieties occur in the Y site for Al, but sometimes occur in the Z site. Prior to accessible chemical analyses, varieties were distinguished by their colour. -As a result, many elbaite mineral specimens were erroneously classified. Today, mineral designations are strictly defined by their chemistry, although some of the historical names live on. The most commonly known gem varieties and their characteristic colour are listed in the table below. -dravite --> elbaite (actual mineral species) --> red colour --> Fe+3 causes the colour -indicolite --> elbaite (mineral) --> blue colour --> Fe+2 and Ti+4 rubellite --> elbaite *sometimes liddicoatite (mineral) --> deep pink to red --> Mn+2 and Mn+3 verdelite --> elbaite (mineral) --> green --> Fe+2 and Fe+3 "chrome" --> dravite (mineral) --> green --> Cr+3, or V+3 canary --> elbaite (mineral) --> yellow --> Mn+2 and Ti+4 Paraíba --> elbaite --> electric "neon" blue --> from Cu+2 -Watermelon tourmaline is a bi-colour variety of this mineral where a bright pink core (from Mn) is surrounded by a grass green rim (usually from Fe). This colour gradient is the result of changing geochemical growth conditions where originally the system was Fe-deficient, leading to the Mn-dominated pink colouration. As the system evolved, Fe became increasingly available to the growing tourmaline thus changing the way light interacts with the Fe-rich portions. Sometimes the rim can also be coloured blue depending on the Ti content of the system. -Paraíba tourmaline is the neon or electric blue gem variety of tourmaline. It was first discovered in the State of Paraíba, Brazil, but that pegmatite source has since run out. -It is the rarest of the precious tourmaline varieties and is also one of the more rare mineralogical varieties of tourmaline due to the unusual Cu content (which sits in the Y site). -A few recent finds of Paraíba-like tourmaline have been reported in Mozambique and Nigeria. We'll read about the Mozambique tourmalines in a later section. Most Paraiba tourmaline is in fact elbaite, though classification of this gem variety is moreso dependant on the presence of Cu rather than being elbaite.

Pleochroism

-Some minerals will display different colours (or saturation of colours) depending on the crystallographic direction of the stone being viewed. -This effect is called pleochroism and is caused by differential absorption of light according to orientation of the crystal - it is best viewed using a simple tool called a dichroscope. -Tanzanite is an excellent example of a pleochroic mineral and displays three colours (often brown, purple, and blue) that align with the three different crystal axes. Iolite (the gem variety of cordierite, page 287 of your textbook) is another example. Its pleochroic colours are typically violet-blue and colourless. -Dichroscope is used to see the different colours related to the different rays in the dichroic synthetic sapphire. In the second image, the pleochroic nature of the faceted trichroic tourmaline can be seen without the aid of any tools.

Describe the geological events that bring diamond from the mantle to the surface

-Sourcing diamonds from underneath 150 km of cold cratonic rock is not an easy task. -Special conditions are required to bring these crystals from deep within the Earth to the surface. -The main mechanism to bring diamonds upwards is kimberlite magmas. -These magmas are generated at the base of the craton (asthenosphere), ascend through the 150 km of crust very quickly, and then erupt in special volcanoes on the Earth's surface. -En route, the kimberlite magmas pick up diamonds that are in their pathway, then deposit them volcanically on the surface. -This process has to be rapid in order to both prevent diamonds from transforming to graphite, as well as exhume them (i.e., to bring to the surface) uncorroded. -The deep-seated magma for these odd volcanic rocks is sourced from the upper mantle and is Fe- and Mg-rich (also termed ultramafic) as well as rich in K (or ultrapotassic) -Kimberlite magmas can also be generated away from diamond-bearing regions below the cratons, but these kimberlites will never carry diamonds. In fact, they are classified as barren kimberlite. -The morphology of kimberlite volcanoes on the surface is tied to their igneous nature as well as the nature of the rocks they are passing through. As the magma ascends upwards through the crust it moves into regions with less and less confining pressure, which then continually allows faster and faster propagation of the magma. -As the magma approaches the Earth's surface it will most likely interact with groundwater. An eruption occurs when hot magma boils water that it comes in contact with, resulting in a rapid and violent expansion of gases. -Although no kimberlite eruptions have been witnessed, the textures found in the rock record support an explosive depositional environment

Total list of countries that have diamond mines and recent stats

-South Africa -Australia -Canada -Russia -West Africa -Angola -Botswana -Congo/DRC/Zaire -SWC/Namibia -In 2015, ~125 million carats of rough diamond were produced globally with an estimated value of $14 billion US dollars ). The majority of these diamonds originate from Africa (e.g, Botswana, Congo, Angola, South Africa and Zimbabwe) with significant amounts coming from Russia, Canada and Australia. In 2015, over 75% were produced by only 4 companies (and their partnerships): De Beers, Alrosa, Rio Tinto, Dominion Diamond. Total cumulative global production of diamonds is estimated to be around 7 billion carats, with nearly 15% of this total production from only the last ~5 years.

Can it be Produced Synthetically? What are its Imitations? (Spodumene)

-Spodumene gem varieties can be synthesized in the laboratory but like topaz and tourmaline, this is not normally done because of an abundant supply of natural material and its "semi-precious" nature. -Spodumene is a relatively low-cost gemstone, so it tends to be the imitator for other higher-end stones, such as morganite or emerald. Pink and green glass are sometimes used as imitations for spodumene, as are synthetic spinel or corundum.

What is its Chemistry and Crystal Structure? (Spodumene)

-Spodumene has the base formula LiAlSi2O6 with significant substitution occurring in both the Al and Li sites. -Kunzite is the result of Mn+3 taking the place of Al and imparting the light pink colour, while the green colour of hiddenite is due to Cr+3 replacing Al. - The red tetrahedra represent Si atoms surrounded by four oxygen atoms, the green octahedra represent Al atoms surrounded by six oxygen atoms and the purple spheres are Li atoms bonded with six oxygen atoms (bonds not shown). -The linking of the Si tetrahedron at apices to form 'chains' is typical of pyroxene minerals and runs the length of the mineral. Similarly, Al octahedron form chains but share edges of their polyhedron, not apices.

What is Spodumene and What are its Basic Qualities?

-Spodumene is a lithium (Li)-bearing aluminosilicate, LiAlSi2O6, and is the base mineral for the gemstone varieties kunzite and hiddenite. -Spodumene is typically colourless, while light pink kunzite is uncommon and vivid green hiddenite is considerably rare. -Spodumene is part of the pyroxene group of minerals, which have the general formula of ABSi2O6 where the total cation charge of A+B must equal +4. Most pyroxene group minerals will have considerable amounts of Mg and Fe, but the geochemistry of pegmatites stabilizes this Li+ and Al+3-rich variety. Like all pyroxene group minerals spodumene forms prismatic crystals with roughly square or rectangular outlines and two distinct cleavages that run parallel to the c-axis and intersect at 90 degrees to one another. -It has a hardness of 6.5 to 7 and a moderate specific gravity of ~3.2. -Refractive indices range from 1.66 to 1.68, and commonly fluoresces under short wave and long wave UV light. -Crystals of spodumene have been mined historically for their Li content. Specimens can reach great lengths with some up to 12.5 m. These weigh more than 50 tonnes.

Can it be Produced Synthetically? What are its Imitations?

-Topaz can be synthesized in the laboratory but like tourmaline, this is not normally done because of an abundant supply of natural material. There is not much that is passed for topaz, except mislabeled species of gem quartz like citrine. Blue bottle glass is sometimes used as an imitation, but topaz itself is more commonly used as an imitation for other less common gemstones.

Can Beryl be Produced Synthetically?

-Synthetic beryl has been produced commercially for a number of years. Several different procedures have been successful in growing sizeable beryl crystals, mostly using a hydrothermal solution. These water-based ("hydro") solutions use hot ("thermal") fluids with the desired chemical components dissolved into them (e.g., Be, Si, Al, and Cr). -When the solution is cooled, beryl crystals will nucleate and if given enough time, clean stones of sufficient size will be grown, faceted, and sold as synthetic emerald. Chatham Created Emeralds and Gilson Emeralds are two such companies marketing synthetic emeralds. -Aquamarine is found in abundant enough quantities and sizes that it is not produced synthetically for retail. However, it is commonly synthesized in laboratories with specific characteristics for academic studies on crystal structures.

Tanzanite

-Tanzanite (Ca2Al3Si3O12(OH) with V replacing Al and Ca) is the main gem variety of the mineral zoisite and is mined mainly from one locality in Tanzania. The mine itself is in the Merelani Hills near the base of Mt Kilimanjaro and is run by Tanzanite One. -Limited amounts of artisanal mining also takes place here and flanks the operations of Tanzanite One to the NE and SW. -The most prized tanzanite has a deep blue-purple colour but is also strongly trichroic, meaning that depending on the angle of viewing it can range in colour, especially when viewed through a polarizing filter (like sunglasses). -For tanzanite, this range is from blue to violet to burgandy-bronze and is the result of vanadium (V2+ and V3+) in the crystal structure. -Since most people are looking for the vibrant blue colour when purchasing gem cutters will purposely orient the direction with greatest blue saturation towards the table of the gem. -Much of the tanzanite mined dominantly shows the burgandy-bronze colour, which is gently eliminated through heat treatment of the rough gemstones in order to enhance the blue-violet colours. -Chromium can also be present in zoisite, however, it leads to a green colouration without the strong notable trichroic properties. -Other colours of zoisite include yellow, pink, dull green and clear varieties although they are not seen as often due to demand. -Tanzanite is orthorhombic (three refractive indices between 1.69 and 1.70), has a hardness of 6.5, a SG of 3.35 and exhibits perfect prismatic cleavage. -Cut tanzanite is normally seen in the <5 carat range, though 15+ carat stones are sometimes seen in higher end jewellery stores in Canada. Per carat pricing is related primarily to colour and then size. -A sorosilicate -Dark blue variety of zoisite which is sometimes mistaken for sapphire -Zoisite crystals are vertically striated and prismatic -Calcium aluminum silicate hydroxide, belongs to the epidote group -Characteristic of regional metamorphism and of hydrothermal alteration of igneous rocks, also found in quartz veins and pegmatites. -Frequently heat treated to remove any brown patches and enhance its colour -Tanzanite crystals have distinct pleochroism, and show gray, purple, or blue depending on the angle from which they are viewed -Cut tanzanites may appear more violet in incandescent light -Comes from Tanzania and Pakistan

Chelsea Filter

-The Chelsea Filter is also sometimes called an Emerald Filter since it is quite effective at discriminating emeralds from other green stones. -It is simply a colour filter that only allows red and green colours to pass through the filter. -It effectively filters out any blue hues of light passing through a stone and gives clues to the true nature of an unknown sample. Each main gemstone variety will show a specific colour or range of colours through the filter, thus adding another piece of information to the list when identifying an unknown.

List the historically important ruby and sapphire occurrences

-The Mogok region of Myanmar (formerly Burma) is the classic origin for natural fine rubies (dubbed Pigeon's Blood Red) while Sri Lanka claims the prize for historically producing the finest natural sapphires, including the Padparadscha variety. -Other famous origins are Kashmiri Cornflower Blue sapphires of Pakistan, as well as Vietnamese rubies. The advent of heat treatment has brought much more gem quality sapphires and rubies to the market from many global localities. This is only possible because non-gem corundum is fairly abundant in certain rock types but rarely is naturally of gem quality (like those from Myanmar or Sri Lanka). The heat treatment allows opaque or translucent stones with poor colour to be upgraded into gem quality corundum. The word "corundum" likely has its root in Sanskrit, derived from "kurunvinda" meaning "hard stone". The origin of the word ruby is likely from the Sanskrit word "ratnaraj", which translates roughly as "king of precious stones". Ruby may have also taken its name from the Latin word for red, "ruber". The Sanskrit word "sauriratna" is most probably the origin of the word sapphire. In ancient Europe, the term "sapphire" was used commonly to describe many blue stones, including some we now know to be topaz or lapis lazuli, not corundum at all. It wasn't until the beginning in the 19th century, when more sophisticated scientific techniques were developed, that rubies and sapphires were found to share a genetic link. Furthermore, many stones of deep colour which had been historically identified as gem varieties of corundum rubies, were found to be red spinel. Two examples of misidentified spinels are the Black Prince's Ruby and the Timur Ruby. The colours for sapphire and ruby are derived from minor impurities in the crystal structure, where other metals have substituted for Al. Specifically, the colours are usually derived by varying amounts of Cr, Fe, and titanium (Ti) with V playing a lesser role. The element chromium imparts a red hue to corundum and in lower concentrations produces pink sapphires. Thus, the distinction between a deeply coloured fancy pink sapphire and a light coloured ruby is somewhat arbitrary.

Raman Microscope

-The Raman microscope is similar to a spectrometer coupled with a microscope but has a number of distinct and fundamental differences. -Raman microscopy is an advanced analytical technique used extensively in the biological and chemical sciences, however, it is increasingly finding its way into other applications, such as mineralogy and gemmology. -It is a rapid and non-destructive technique that does not require physical preparation or physical contact with the sample in question, making it ideal for faceted gemstones that are set in jewellery. -The microscope is outfitted with a monochromatic laser (normally tuned to a wavelength of 532 nm) which is directed at the sample, and some of the light is scattered back towards the microscope CCD detector. -The scattered light will be imparted with a diagnostic pattern according to the chemical makeup and structure of the target, and is fairly easy to interpret. It therefore allows for fairly conclusive identification of a gemstone's mineralogical ID.

Describe the Kimberley Process

-The World Diamond Council, formed in 2000, is one of many organizations involved in the monitoring of the diamond industry. The Council's original mandate, which has now become known as The Kimberley Process Certification Scheme (KPCS, also simply known as the Kimberley Process), was: -"to address the development, implementation, and oversight of a tracking system for the export and import of rough diamonds to prevent the exploitation of diamonds for illicit purposes such as war and inhumane acts" -This applies to rough diamonds -This mandate includes the elimination of Blood or Conflict diamonds. -The process officially endorses stable countries and allows them to produce (which includes mining, cutting, or polishing) conflict-free diamonds. -These conflict-free diamonds are tracked in parcels and can only be sold to other countries that are also endorsed as conflict-free, and provided that they too have strict regulations for exporting and importing rough and polished diamonds. -By facilitating the trade of legitimate stones, the Kimberley Process has significantly reduced global trafficking of conflict stones. The Process has provided more confidence to retailers and consumers that they are not supporting illegitimate mining operations. -The Kimberley Process is not simply a collection of international laws, but rather an agreement between the major diamond mining, exporting, and importing countries and companies. -In total, 81 countries are involved as of August 2013, some of which have more significant impacts than others. -For example, the United States imports huge volumes of diamonds and therefore has a very significant impact on the success (or failure) of the consumption aspect of the Kimberley Process. -Conversely, poverty stricken regions with diamond production can significantly impact the success (or failure) of the Kimberley Process through proper implementation and regulation in areas that are prone to illicit diamond trade. -Other countries that neither produce diamonds nor import significant volumes of diamonds will not have a significant impact on the success (or failure) of the Kimberley Process. -It is the cooperation amongst all the countries involved that gives the Kimberley Process its strength. Assisting the World Diamond Council in ensuring the validity and effectiveness of the Kimberley Process are other non-governmental organizations that are involved more specifically with human rights issue, notably Global Witness and Partnership Africa Canada.

Corrosion

-The abundance of volatiles associated with highly fractionated magmas can unfortunately be detrimental for early stage gem minerals in pegmatites. (explosive) -When these volatile elements are present at the end of a pegmatite's life, the geochemical environment that they create may be corrosive to earlier formed minerals. As a result, the early minerals can be partially or completely corroded and replaced with minerals of similar composition, but greater stability under these late-stage conditions. -A common example of this is beryl, which is sometimes found in resorbed "bullet" shapes alongside other beryllium-rich minerals such as bertrandite. Spodumene often gives way to lepidolite, and tourmaline gives way to clays and micas. -Corrosion also leads to the development of pegmatite pockets, however, since the fluids are very corrosive they tend not to produce significant amounts of gem material.

Describe the mineral formula and crystal structure of corundum

-The base chemical formula for corundum is Al2O3. The aluminum (Al) in this simple formula is the key to generating the striking colours of corundum's gem varieties. -Aluminum can be replaced by many of the transition elements, which are common chromophores (colour causing elements) in minerals. -Each Al atom in the crystal bonds with six O atoms in the form of an octahedron. These Al octahedrons share some of their corners, edges, and faces with each other and consequently it is more intuitive to view the crystal structure of corundum using the ball and stick method instead of polyhedral method.

Quartz Gems

-The base formula of the quartz group of gems is SiO2, but the ubiquity of this base mineral group and the large number of variations give rise to no less than a dozen gem varieties. The most precious of the group is opal; other popular varieties include amethyst, citrine, and agate. -Quartz crystal forms range from giant euhedral crystals of quartz in pegmatites (up to ~6 m long and 1.5 m across) down to cryptocrystalline varieties like agates where it would be tough to find individual crystals even under a microscope. Because of the commonness of these gems and their global distribution, they have been used by most of the world's civilizations and cultures in some way or form. -Their "upper intermediate" hardness (Mohs = 7) makes quartz harder than many materials, but soft enough that it could be carved and fashioned efficiently. Many carved quartz artifacts are dotted throughout antiquity and include basins, bottles, boxes, rings, cameos, statues, beads, and skulls. The pages in the textbook will guide you through the wonderful diversity of quartz's gem varieties. -1) ROCK CRYSTAL -Colourless, transparent variety of quartz. -Vessels of all kinds and spheres have been carved from large crystals since ancient times, and the name rock crystal emerged in the late Middle Ages to differentiate it from newly perfected colourless glass. -Quartz is silicon dioxide, the third most common mineral in Earth's crust after ice and feldspar. -Quartz comes in 2 forms: crystalline or fully crystalline; and cryptocrystalline, formed of microscopic crystalline particles. Crystalline quartz is usually colourless and transparent (rock crystal) or white and translucent (milky quartz) but it can also occur in many coloured varieties. Crystallized impurities occur in some crystalline quartz varieties, such as the hairlike inclusions of rutile, needles, or green mosslike clumps of chlorite. Quartz occurs in nearly all silica-rich metamorphic, sedimentary, and igneous rocks. The optical properties of rock crystal led to its extensive use in lenses and prisms, and as an inexpensive gemstone.

Diamond growth pic

-The cartoon diagram of the Earth's crust (above) shows an old craton with a deep keel, the outline of which is indicated by a blue line. -The Stability Zone separating diamond from graphite is indicated by the dashed white line: below the line diamond is the stable C mineral, whereas above it, graphite is the stable C mineral. - The red dots indicate areas where igneous magma is being generated and the red chevrons (V-shaped patterns) indicate where magma has accumulated. -Note how even though igneous rocks formed at mid-ocean ridges and along subduction zones are sourced from the same general magmatic region, they are generated above the diamond-graphite line, resulting in the production of only graphite, the stable C mineral. -This Temperature-Pressure diagram highlights the relationship between the two carbon minerals; graphite and diamond. The area in red indicates the typical pressures and temperatures in cratonic lithosphere, whereas the area in green indicates the typical temperatures and pressure in the asthenosphere. -Diamonds will only form in the *lithosphere (not the asthenosphere), so the "fertile" region for diamonds is a small window (yellow area) within the lithospheric region below the diamond-graphite line.

What is its Chemistry and Crystal Structure?

-The crystal chemistry of the tourmaline group is complicated; some refer to it as a "garbage bag" mineral because so many different elements can enter into the structure. -The base tourmaline formula and the formula for schorl (the most common variety) are: BORO SILICATE base: XY3Z6(BO3)3Si6O18(OH)4 schorl: NaFe3Al6(BO3)3Si6O18(OH)4 -In the base formula, the letters X, Y, and Z represent crystallographic sites with variable composition. Schorl and the other 13 accepted varieties of tourmaline result from different combinations of constituents in these three sites. For schorl, the X site is filled with Na, the Y with Fe, and the Z with Al. -The Si6O18 grouping represents vertically stacked but isolated rings comprising 6 Si tetrahedron linked together on their corners. The BO3 grouping represents the essential boron (B) that is linked with three oxygen and which is also stacked vertically along the c axis. The three cations that sit in the Y sites cluster together, perched on top of the Si6O18 rings. The Z site, which is typically occupied by Al, forms an inter-penetrating linked network that separates each column of Si rings from each other. The X and OH groups in the structure occupy the space between repeating units of Si rings and Y site clusters. -The other main varieties of tourmaline are classified according to the element occupying the X site: alkali tourmaline (X=Na), calcic tourmaline (X=Ca), and vacancy tourmaline (no X-site cation). -Most gem varieties belong to the alkali tourmaline group and arise from different transition metals in the Y site. -The mineral elbaite is the most common for gem varieties of tourmalline and it has both Li and Al in the Y site. -Colourless elbaite is sometimes called by its historical name, achroite. Liddicoatite is the next most common tourmaline group mineral that produces gem quality crystals.

Describe the global distribution of diamond deposits, geographically and geologically

-The current understanding of diamond deposit geology is far beyond that of even 20 years ago. -Consequently, the distribution of known diamond deposits is becoming better documented and the exploration for new deposits is rapidly becoming more refined. -Cutting edge research is used in the diamond industry during exploration and mining, however, publishable peer-reviewed research findings typically lag behind due to confidentiality clauses and as well as access to sites, samples and information. -As we learned in Lession 10.1, diamond-bearing kimberlites occur exclusively in areas with "old" and "cold" Archaen-aged (older than 2.5 billion years) cratonic basement rocks, such as the cratons of the Canadian Shield or the Kaapvaal craton of southern Africa. By focusing on these Archean-aged cratons (sometimes known as Archons) we can draw a map of the most relevant areas with diamond potential. -Many historical diamonds originated from India with Brazil becoming a somewhat significant source in the 18th century, and then of course South Africa's important role in the diamond industry starting in the 19th century. -It should be no surprise then that each of these geographical areas have regions of Archean cratons (red)! -Following South Africa in the 20th century, significant diamond-bearing kimberlite discoveries were made in Russia, Australia, Canada and other regions of Africa. -Many of these are shown on the following map of the world, which also includes major diamond mines and basement rock types. -With only ~30 active major mines and advanced projects from primary "in-situ" kimberlite sources in the world, the diamond industry collects the bulk of its rough material from a relatively small number of companies and locations. -Particularly notable is the fact that many of the mines are located in Africa, which has a turbulent past and uncertain future stability.

Dichroscope

-The dichroscope is a useful tool for determining what *optic class* a mineral or gem belongs to. -It capitalizes on optical effects generated from gems with two or three indices of refraction when light is transmitted through the stone. -It's essentially a tube in which two dichroic filters are set next to one another, but oriented 90 degrees from one another; these are usually made of calcite. -The resulting effect is that stones with more than one refractive index (i.e., any material that is not isometric) will show two different hues through the two different filters (seen as little rectangles through the scope). -Stones with only one refractive index (i.e., any mineral in the isometric crystal system, e.g., diamond or spinel) will only show one colour. -This quickly differentiates these two classifications of minerals. Furthermore, the specific colours and tones seen through the dichroscope of dichroic (e.g., sapphire) and trichroic (e.g., tanzanite) minerals can also be diagnostic to a trained observer. -With a hand lens, Chelsea filter, and dichroscope, nearly 90% of all gemstone varieties can be identified.

Ruby vs Sapphire prices per carat

-The following tables are estimates of prices per carat for "Good" rubies and sapphires from "non-prime sources" based on size (prices accurate as of ~2007). Note how the value per carat increases with increasing size. Rubies: Less than 0.5 carats $25 to $350 0.5 to 1.0 $350 to $600 1.0 to 2.0 $600 to $2500 2.0 to 5.0 $2500 to $4500 More than 5.0 $4500 to $8000 Sapphires: Less than 0.5 $175 to $200 0.5 to 1.0 $200 to $350 1.0 to 2.0 $350 to $600 2.0 to 5.0 $600 to $1000 More than 5.0 $1000 to $2500 Sapphires are less highly priced than rubies for all weights other than less than 0.5 carats, for these sizes, sapphires are 175-200 while rubies are 25-350 -Record setting prices for rubies and sapphires rival prices (on a per carat basis) of the finest diamonds. A fine Burmese ruby weighing 8.62 carats and set in a gold Bulgari ring sold at a Christie's auction in 2006 for $3.6 million USD. That works out to about $425,000 per carat! An interesting quote by J.B. Tavernier (a famous historical gem trader) written in 1676 was included in the item's description for the auction. It still holds true today, almost four hundred years later: "When a ruby exceeds 5 carats, and is perfect, it is sold for whatever is asked for it." In 1993 a much larger ruby (38.12 carats, loose) was sold at auction for $5.9 million USD, at approximately $150,000 per carat. Of recently sold fine sapphires, a 42.28 carat Kashmir sapphire was auctioned by Christie's in 2008 for $3.5 million USD, a per carat price of approximately $82,000. A smaller (22.66 carats) but finer stone fetched about $3 million USD in 2007, which is approximately $135,000 per carat. A fine 10.14 carat Padparadscha sapphire was sold in 2004 for $250,000 USD, or approximately $25,000 per carat.

UGRANDite vs PYRALSPite

-The garnet group is composed of six main minerals divided into two main mineral series, ugrandite and pyralspite. The series names are taken from the minerals included in each group: UGRANDite for Uvarovite, GRossular, and ANDradite PYRALSPite for PYRope, ALmandine, and SPessartine. -All of the ugrandite series garnets contain essential Ca in the structure, while those of the pyralspite series require Al in their structure. -The minerals of the garnet group show a wide range of colour from "ruby red" to "emerald green" (among others) and also have good hardness. Garnet itself is quite a common mineral, but the gem varieties are uncommon to rare, with tsavorite and green demantoid garnets fetching up to ~$3,000 USD per carat for stones under 3 carats. -Garnets are widespread minerals, particularly abundant in metamorphic rocks -They form in many different colours but garnets are easy to recognize because they are generally found as well-developed crystals in cubic crystal form -There are 15 garnet species, all conforming to the general formula A3B2(SiO4)3, where A can be calcium, ferrous iron, magnesium, or manganese, and B can be aluminum, ferric iron, chromium, manganese, silicon, titanium, zirconium, or vanadium. -Name of an individual garnet is given is the name of the end member that makes up the largest percentage of its composition. -Garnets are all cubic, usually occurring as dodecahedrons, trapezohedrons, or a combination of the two.

Scratch Pad and Hardness Picks

-The hardness and streak of a gem is not easy to determine because it would require destructive techniques. For mineral specimens, however, there is usually enough material that some can be sacrificed to determine hardness and streak colour. -Streak colour is independent of the mineral's apparent colour and can easily give away certain minerals, such as hematite. -We test streak colour by rubbing the mineral in question against a white ceramic plate (H=~6.5). If the mineral is softer than the plate, it will leave a streak of its powdered material on the white backing; the colour of the streak can be used to narrow down the possible mineral identities. -Gem minerals tend to be harder than 6.5 and consequently streak plates are not always useful since a mineral harder than 6.5 will actually scratch the streak plate instead of vice-versa. -In this case we can use known examples of other minerals to determine relative hardness, or we can use specially made "pencils" tipped with materials of known hardness. -By finding out which known materials can and cannot scratch the unknown we can then determine the range of hardness that the unknown mineral must have. -This is especially useful, for example, to determine whether a clear hexagonal mineral is quartz (H=7), beryl (H=8.5), or corundum (H=9).

Geochemical Families

-The high concentrations of rare element and the resulting mineral assemblages facilitate the classification of pegmatites. The concept of geochemical families for pegmatites was recognized many years ago, but the most commonly used scheme was introduced by Černý in 1991. In Černý's scheme, pegmatites are divided into four main groups based on three main factors: 1) depth of emplacement below the surface; 2) range of temperature; and 3) type of rare element enrichment These three variables control what mineral phases can be present in a given pegmatite since mineral phases will only be stable in specific conditions. Based on the variables above, the four pegmatite groups are: 1) Abyssal (high temperature, variable pressure); 2) Muscovite (low T, high P); 3) Rare-element (low T, low P); and 4) Miarolitic (medium T, low P) Of these four groups, rare-element pegmatites tend to produce the most gemstones. This group is further divided into two categories, 1) Lithium-Cesium-Tantalum ("LCT") 2) Niobium-Yttrium-Fluorine ("NYF") based on the dominant rare elements. Between the two subdivisions, LCT pegmatites give rise to the most gem minerals. -All pegmatites contain large amounts of gases and volatiles that are effective fluxes for the pegmatite magma. -Fluxes are elements and/or compounds that reduce the freezing point of the magma. -Lower freezing points result in more time for crystal growth. Fluxes also decrease nucleation, which result in fewer crystals, and increase movement of elements to where crystals are growing, which result in bigger crystals. In many pegmatites, the collection of fluxing agents include H2O, F, Cl, carbonate (CO3)-2, borate (BO3)-3, Li, and phosphate (PO4)-2.

Describe the mineral formula and crystal structure of beryl

-The ideal chemical formula for beryl is Be3Al2Si6O18 - an aluminous beryllium cyclosilicate. -The dominant crystal sites are the tetrahedral sites of Si and Be, the octahedral site of Al, and a distinct channel located along the length of the c-axis within the six-membered rings comprising SiO4 tetrahedra. -With respect to gem beryl, substitutions in the octahedral Al site are the most important because they give rise to the most vivid colours. Almost all beryl crystals contain at least minor substitutions that result in the variety of colours displayed by this single mineral. -Crystal structure of beryl looking just off the c axis, along the orientation of the channels. In this model, red triangles represent the Si tetrahedron (1 silicon atom surrounded by 4 oxygen atoms) arranged in rings, purple Be tetrahedrons (1 beryllium atom surrounded by 4 oxygen atoms), green Al octahedra (1 aluminum atom surrounded by 6 oxygen atoms), and blue spheres are usually Na or water residing in the channel site. -Crystal structure of beryl looking perpendicular to the c axis, note the sequential stacking of Be and Al polyhedra with Si polyhedra that gives rise to the basal cleavage of beryl. -Beryl adheres to the constraints of the hexagonal crystal system (see page 100 in your text), giving it one primary c axis, and three secondary a axes on a single plane, all separated by 120 degrees. This figure shows a depiction of the hexagonal crystal system, how a simple prism would be represented in this system, and that simple hexagonal prism superimposed on a real beryl crystal. -Although beryl ideally consists of only four elements and its elemental substitutions can be relatively straightforward, a comprehensive understanding of this mineral remains elusive. Historically it has been difficult to develop conclusive statements regarding exactly what element exchanges are occurring because it is difficult to obtain accurate measurements of Li and Be (These elements are simply just tricky to work with.) Furthermore, the similarities between the Si and Be tetrahedral sites makes it difficult to determine where exactly substituting cations are going.

Polarizing Microscope

-The polarizing microscope is similar to a normal microscope but has a number of distinct differences. -First, it is designed primarily to view rock samples that have been sliced to 30 microns in thickness, which are known as thin sections of rock. -Next, it has a series of special filters that allows the user to polarize and change the light passing through the minerals in the thin section while observing how that light interacts with the individual minerals. -Last, it has a rotating stage, variable focus, and high magnification (up to ~400X). These microscopes tend to be very expensive and are most often found in university laboratories. They are sometimes called petrographic microscopes and used primarily for studying the origin of rocks.

How Large Does Beryl Get?

-The largest beryl crystals undoubtedly originate from pegmatites. Pegmatites provide a geological environment that facilitates the diffusion of the necessary elemental components (e.g., Be, Al, and Si) to form large beryl crystals. Large beryl crystals have been reported from numerous localities, including areas in Madagascar (many areas), Russia (Ural Mountains), and the USA (East and West coasts). Single crystals have been measured up to 18 m long and 3.5 m across, with estimated weights in the hundreds of tons! -One of the largest uncut emeralds of gem quality is the Guinness Crystal, now part of the collection of the Banco Nazionale de la Republica in Bogota, Colombia. The Guinness emerald crystal weighs 1795 carats and exhibits exceptional clarity and colour making it not only a large specimen, but also a very valuable one. -The fine emeralds from Colombia, as noted before, are hosted in an unusual environment for Be enrichment. The size of the resulting quartz veins and the dynamic nature (during tectonic activity) of the vein formation limits the upper end of the scale for the size of stones. One of the largest cut emeralds is a 75.47 carat Colombian beauty and is called the Hooker Emerald. It is housed in the Smithsonian Institution in Washington D.C., USA. -Exquisite aquamarines are also found in historical pieces of jewelry, typically the possessions of royalty. One such example is a 10-cm long sword handle weighing in at over 400 carats, once belonging to Joachim Murat, a French cavalry commander. An exceptionally large and flawless golden beryl from Brazil is in the collection of the National Museum of Natural History in Washington DC and weighs an astonishing 2054 carats! In general, aquamarine, heliodor, morganite, goshenite and pale green beryl (not emerald) exhibit the largest size crystals in the beryl family. -Emeralds of gem quality that qualify as exceptionally large are in the 50 carat range, while exceptionally large red beryl is in the 5 carat range.

Why is Gem Corundum rare?

-The mineral corundum itself is not particularly rare and there are many different geological models that have been postulated for explaining gem corundum occurrences. -However, the most sought after intensely coloured rubies, pink sapphires, and blue sapphires are still quite rare in these many environments, especially if untreated (Recall from a previous lecture... what is the most common treatment for corundum?) Additionally, the durability and historical significance of gem corundum continue to make this mineral an important coloured gemstone. -The cornflower blues, pigeon's blood reds, and hot pinks are all difficult colours to generate in natural untreated specimens. This is because there are many variables that need to coincide to ensure a premium colour. -For example, if Cr-bearing rubies or pink sapphires contain any appreciable amount of Fe or Ti, their hue will shift from a pure red towards purples and blues. Still a nice colour, but much more commonplace. -Pure velvety cornflower blue colouration, on the other hand, is not necessarily due to uniformity of substituting elements, but rather to fine inclusions. The inclusions are tiny bubbles of fluid and gas within the crystal, too small to be seen with the naked eye, but large and pervasive enough to disperse light entering the stone. This softens and deepens the resulting colour and imparts a "sleepy" look.

What are Common Treatments for Beryl?

-The most common treatment for emeralds is oiling. Oils with a similar refractive index to beryl, such as cedarwood or palm oils, are often forced into cracks of the stone. -When oil with a refractive index (~1.6) matching that of beryl fills the stone's air spaces (refractive index of air ~1), the stone appears less flawed and consequently commands greater value. -Some new polymers with a matching refractive index are being used in emerald treatment to not only improve clarity, but also to add durability to the stones. -Some of these polymers are patented and also purposely contain fluorescent components so that gemologists will be able to quickly tell if the stone has been treated. Emerald specimens still attached to the matrix (host rock) are sometimes repaired using epoxies if breakage has occurred. -Rough beryl of mediocre colour is often heat treated to bring out the blues, resulting in an abundance of aquamarine in the market. - -Undesirable green and yellow beryl contains oxidized iron (Fe+3); when heated, the iron in the crystal structure gets reduced to Fe+2 (i.e., it gains an electron), which imparts the stone with a lighter blue colour.

Non african mines history

-The opening of the first significant non-African mine, the Mir Diamond Mine in Russia, was in 1957 shortly after its 1955 discovery. Annual production from Mir by Alrosa Mining Corp quickly reached ~5 million carats and by the mid 1970's it was producing nearly 10 million carats annually. This non-DeBeers mine was the *first major blow into the previously established and very strong DeBeers monopoly.* Following Mir were a series of additional Siberian mines: Udachnaya (1976), Jubileynaya (1997) and Nyurba (2004). -The next significant event in global diamond mining was the opening of the Australian Argyle Diamond Mine by Rio Tinto in 1983 after the discovery of the "non-traditional" diamond-bearing *lamproite* in 1979. Australia's annual production started at ~30 million carats, a good proportion of the market share by volume at that point but much of those diamonds were of industrial quality (ie, non-gem quality). In fact, in 1994 the Argyle Mine produced 40% of the world's diamonds by volume! This was the *second significant shift of DeBeers' global monopoly and together with the Siberian diamonds was a significant shift in the global diamond trade.* -Finally, Canada entered the global diamond trade in 1998 with the opening of Ekati (BHP Billiton), followed by Diavik (Rio Tinto) in 2003. Interestingly enough, &neither of these early Canadian mines are operated by DeBeers despite intense but unsuccessful exploration by DeBeers in Canada during the previous ~3 decades*. - Just years after startup, Ekati was producing ~5 million carats annually and Diavik showed similar productions also with ~5 million carats annually after a few years of operation. -Since then production has been relatively steady and the *diamonds produced from the Canadian mines tend to have a higher average value per carat when compared against other nations with similar production volumes*.

Refractive index

-The refractive index, n of a medium (such as a gemstone) is a measure of how much it will refract light of a specific wavelength passing from a vacuum into the medium in question. -In other words, the refractive index measures how much the incident light is slowed when it enters a new medium compared to when it travels in a vacuum (where the refractive index is, by definition, equal to 1). -Note that the refractive index of a medium is also dependant on wavelength - this is important for dispersion (L12.8). -Refractive indices of minerals and gemstones are used as diagnostic features in identification. Diamond's refractive index of 2.419 quickly sets it apart from regular glass with a refractive index of 1.5. -When cracks or fissures are present in a rough gemstone, gem dealers will often attempt to fill them with an epoxy to strengthen the stone. This allows the material to be faceted into a larger gemstone. If the refractive index of the epoxy is not matched with the host mineral's refractive index, the epoxy's different refractive index will cause the light traveling within the stone to refract (or bend). Because gemstones are normally homogenous, the refraction of light inside an 'epoxied' stone will be atypical and distracting, taking away from its value. If the epoxy's refractive index matches that of its host, no refraction will occur and the filler material will be optically undetectable. Consequently, a great deal of effort is invested in order to ensure that the refractive index of an epoxy matches that of the mineral that it is strengthening.

Explain the differences between the different gem beryl varieties (e.g., beryl, emerald and aquamarine)

-The resulting colour of a beryl crystal is usually closely tied to substitution into the octahedral sites of the mineral structure normally occupied by Al. As with most cation substitutions, the chromophores that typically take the place of Al need to be similar in charge and ionic radius. -This effectively reduces the number of possibilities for elements that may be able to enter into the crystal structure. Deviations at the channel site and Be-site from the ideal base formula are sometimes the cause of colours, too. -The most familiar example of coloured beryl occurs when Cr+3 substitutes for Al+3, imparting a vibrant green colouration and generating the variety of beryl known as emerald. It is generally agreed upon that the light blue colour of aquamarine is a result of Fe in the Al site, but there are some nitty-gritty complications once you start digging deeper. -Research has shown that the "Maxixe-type" (often pronounced Ma-Sheesh-Ay) beryl, which has been found only in Minas Gerais, Brazil, shows a dark saturated velvety blue and owes its blue colour to irradiation and the presence of the radical nitrate (NO3-) in the channels. Unfortunately, its colour fades upon exposure to light, eventually rendering the crystal to a pale blue.

Spectroscope - Pocket and Benchtop Models

-The spectroscope is a specialized gemological tool that is used primarily to differentiate specific stones from one another when results from other tests are not conclusive. -The concept behind a spectroscope is based on absorption of light transmitted through the gemstone. -White light passing through a stone will have some of its spectrum absorbed. As this transmitted light passes into the spectroscope tube it is separated out into its spectrum of colours by a prism or diffraction grating. -Where a specific light has been absorbed by the material, dark spots will appear on the spectrum. The specific bands of light that are absorbed are characteristic for specific gemstones. Compendiums of absorption spectra are compiled in reference books for gemologists. -These tools come in both pocket size and bench top models. Pocket-sized spectroscopes are usually not considered quantitative but to a gemologist with a good understanding of the anticipated spectra of gemstones, certain species can be ruled out quickly if characteristic absorption lines are not present.

Describe the difference between nephrite and jadeite

-The term "jade" in today's usage refers to two different and highly valued translucent rocks: jadeite and nephrite. -These are gems of high durability and a wide range in colours (not just the familiar green). -Historically, the term "jade", including it's various names in different cultures, referred to a number of durable stones such as serpentinite, that had similar uses as jade but were of different mineralogical compositions. -Mineralogically, nephrite is actually a mass consisting primarily of finely crystallized (microcrystalline to cryptocrystalline) amphibole with a composition between tremolite to actinolite (Ca2(Mg,Fe)5Si8O22(OH)2). -Jadeite is a rock (i.e., polymineralic) comprised primarily of the pyroxene mineral jadeite (NaAlSi2O6). Jadeite is often described as having a granular texture and nephrite a silky texture, a direct result of the fibrous nature of amphibole and blocky texture of pyroxene. The translucency of jade is often evaluated by the maximum thickness required to allow significant light through the stone. Translucency is sometimes called the ventana (Spanish for window). -Jade has been treasured by many cultures, perhaps most notably the Chinese and the Maori of New Zealand. The earliest record of jade being used as tools dates back almost 5,000 years in Asia and Europe. Artifacts dating much further back have also been found. There are many occurrences of jade in the world and they appear on every continent. -British Columbia produces a large amount of nephrite jade and exports considerable amounts, especially from the Cry Lake and Dease Lake regions. Although there are many showings and occurrences throughout the province, other significant regions include Cassiar, Mount Ogden, and Bridge River.

Carat

-The total weight of a stone is measured in carats. One carat is equal to 0.2 grams; 5 carats is equal to 1 gram. -Jewelers or gemologists may also speak of points, where 1 point is 0.01 carats. Thus, a half carat stone (0.5 carats) is 50 points and a 1 carat stone is 100 points. Weights are usually recorded to the second decimal point, however, measurements with 3 decimal points are also common. -As one can imagine, the larger the stone the more valuable it is. -However, because stones of big and bigger sizes become progressively more rare, value is clearly not linearly related with size. -For example, a 1 carat stone will be worth more than twice a 0.5 carat stone that has the same cut, clarity, and colour. -Stones of above 3 or 4 carats are still within the price range for consumers while a great increase in price is expected from that point up to about 7 carats. -Beyond that, the price of larger stones (i.e., 10 carats and up) increases at a slower rate. Note though that the price of diamonds can fluctuate considerably depending on the global production of diamonds and the prevalence of larger stones.

What Does it Look Like Rough?

-The typical tabular pyroxene shapes is quite prominent with spodumene gem varieties, as are the two cleavages associated with the pyroxene mineral group.

Jadeite

-There are two different minerals that are commonly called "jade": jadeite and nephrite. -Jadeite is a mineral in its own right, a pyroxene. -Nephrite, an amphibole, is a variety of tremolite or actinolite. -Jadeite is made of interlocking, blocky, granular crystals whereas nephrite crystals are fibrous. It's a rock -These two differing textures can sometimes help distinguish between them: nephrite often appears fibrous or silky; jadeite commonly has a more sugary or granular texture. -Crystals of jadeite do occur but are very rare. They are usually found in hollows within massive material, and are short prismatic in habit. -Jadeite appears in a number of colours, whereas nephrite has a much more limited colour range. -Pure jadeite is white. Its other colours include green, coloured by iron; lilac, coloured by manganese and iron; and pink, brown, red, blue, black, orange, and yellow, coloured by inclusions of other minerals. Emerald-green jadeite is coloured by chromium and is called imperial jade. -Jadeite generally occurs in metamorphic rocks with a higher-pressure origin than nephrite, although it has been found in lower pressure metamorphic rocks. -Usually recovered as alluvial pebbles and boulders, but is also found in rocks in which it originally formed. Widespread in metamorphic rocks formed at subduction zones. -Weathered jadeite typically develops a brown skin, which is often incorporated into carvings -Frequently has a dimpled "orange-peel" when polished -Myanmar is a major source of jadeite and in particular imperial jade -Japan and California are also sources -Other green stones often misnamed "jade"

Nautiloids and Ammonoids

-These 2 groups of cephalopods are among the most advanced mollusks. -Ammonoids evolved from nautiloids, which appeared during the Ordovician. Only a single genus of nautiloid survives today, the pearly nautilus. -Nautiloids and ammonoids are both characterized by a series of internal chambers that permitted the animal to control its own buoyancy. All the chambers were connected by a central stem called a siphuncle. Most were good swimmers, and were scavengers, carnivores, or both. In general, nautiloids can be distinguished from ammonoids by the pattern formed by their sutures, the seams between their chambers. -In nautiloids, the line of the sutures is straight or gently curving. In ammonoids it is highly complex and often appearing fernlike. The ammonoids emerged in the Devonian, and became extinct at the end of the Cretaceous. They evolved rapidly, and are good fossils for dating Late Paleozoic and Mesozoic rocks. Organic Gems are generated by organic (biological) processes and are judged by the same criteria as gemstones of mineral origin: beauty and durability.

UV Lamp

-These lamps emit light in the ultraviolet (UV) portion of the electromagnetic spectrum. They generally come in two types; short wave and longwave. -Short wave UV lamps emit peak intensity around ~260 nm while longwave lamps emit peak intensity around ~365 nm. -All conventional UV lamps are mounted with fluorescent tubes and many come with two tubes: one that emits longwave and one that emits short wave radiation. Long wave UV light emitting diodes (LEDs) are also becoming more common in the marketplace. -UV lamps are used to observe UV fluorescence (under short wave and longwave) in gemstones and minerals, a diagnostic feature of many minerals. -Certain minerals under UV radiation (which has a more energy that visible light) re-emit the radiation at a lower energy level. If the energy level of the emitted light is in the visible realm, then our eyes will be able to detect it. This re-emitted light is called UV fluorescence. -The word "fluorescence" comes from the mineral fluorite, which displays this behaviour under UV radiation.

The Lore of Emerald

-To the Egyptians, emeralds were a symbol of fertility and life -The Aztecs called emerald quetzal itzli and associated it with the quetzal, a bird with long green plumage - a symbol of seasonal renewal -In Europe, alchemists regarded emerald as the stone of Mercury (Hermes) - messenger of the gods and conductor of the souls of the dead -When held in the mouth, emerald was believed to cure dysentery and was worn as a preventive for epilepsy -It was also said to assist women in childbirth, drive away evil spirits, and protect the chasity of the wearer -It was held to have great medicinal value if administered internally, and in particular good for eyesight -In the 17th century, Anselmus de Boot, physician to the Holy Roman Emperor, recommended an amulet of emerald to prevent panic, cure fever, and stop bleeding -Unfortunately, emerald was also considered to be an enemy of sexual passion -Albertus Magnus, writing in the 13th century, noted that when King Bela of Hungary embraced his wife, his magnificent emerald broke into three pieces

What Colours can Topaz Have? How are These Colours Generated? What Gem Varieties Result?

-Topaz comes in a more limited range of colours than tourmaline, but still shows quite a variation and is colourless when pure. -After colourless, lightly coloured brown, blue, and yellow are the most common colours; while pink, red and orangey-red are more rare. -"True" Imperial topaz has a vivid reddish-orange colour, however, this variety name has been commonly misapplied to duller cognac coloured topaz. -The range of colours often referred to as "Imperial Topaz". The colour of Classic Imperial Topaz would be on the right side of this spectrum. -Colours are mostly generated from *colour centers in the crystal*, where single "free" electrons sit in holes generated by site vacancies normally occupied by F. -These colour centers can be natural and form during crystal growth or generated from irradiation either naturally from radioactive minerals or treated in the laboratory. -Imperial topaz is the most valued of the varieties and were originally sourced from the Ural Mountains of Russia. Today, most of the production of Imperial topaz, or near-Imperial topaz, comes from the Ouro Preto mine in -Brazil. Fine pink topaz from northern Pakistan is also well-known.

Total internal reflection

-Total internal reflection is an important property to consider for faceted gemstones. -When light travels from a medium with high refractive index (gemstone) to one with low refractive index (air), total internal reflection can occur if the angle of incidence is greater than the critical angle . -The value of the critical angle is dependent on the refractive index of the gemstone and surrounding material. The critical angle defines the angle of incidence above which total internal reflection occurs. -This phenomenon is particularly significant in diamonds. Diamonds, which have a high refractive index of 2.419, are faceted with specific angles and proportions to maximize the amount of light that undergoes total internal reflection. -Maximum brilliance of a stone is achieved when much of the light that enters the crown facets reflects from the lower pavilion facets and then re-emerges from the crown to our eyes! -Incident light can refract and reflect (red rays) if the angle of incidence is less than the critical angle, or undergo total internal reflection (blue ray) if the angle of incidence is greater than the critical angle. -Light rays are reflected back from the facets of a gemstone at angles to the normal (N) which are greater than the critical angle, and are refracted back out of the gemstone at angles less than the critical angle -Similarly, the lower diagram shows light undergoing reflection (I1), refraction at the critical angle (I2) and refraction (I3) out of the gemstone. - If light is incident along "Normal" it would simply pass through. -Faceted quartz and diamond are good minerals for investigating this phenomenon (see figure below) because they are common 'colourless' gem materials with significantly different optical characteristics .=The probability that light rays will undergo total internal reflection in faceted quartz and diamond of roughly equivalent dimensions and angles, varies because the refractive index of these two minerals is different and as a result their critical angles are different. So the ability of these two minerals to accept and return light back up through their crowns' is also different. -Diamond has a lower critical angle than quartz. As a result for diamond, there is a greater range of incident angles of light that can be redirected back through the gemstone's crown rather than go through the pavilion. The end result for the human eye is diamond's superior brilliance. When the angle of incidence is less than the critical angle, it will be refracted out of the stone. -So when the critical angle of a gemstone is large, there is a greater chance that light will be refracted out of the stone rather than internally reflected. One way to increase the amount of total internal reflection in a gemstone with a large critical angle is to deepen its pavilion and thus modifying the incident angles.

Can It be Produced Synthetically? What are its Imitations?

-Tourmaline can be synthesized in the laboratory but this is not normally done because of the abundant supply of natural tourmaline. -Paraíba-type, indicolite, and rubellite tourmaline are the most commonly imitated varieties since they command the highest prices. Spinel, bottle glass, and amethyst are the most common material passed for these varieties of tourmaline.

What is Tourmaline and What are its Basic Qualities?

-Tourmaline is a complex borosilicate mineral group with hexagonal (trigonal) symmetry. It typically occurs in long slender crystals with a pseudo-hexagonal outline and euhedral crystals are common. -Vertical striations down the crystal face are very common and can sometimes be used as a diagnostic feature. -It has two poor cleavages, so when the stone breaks the surface is quite uneven. -It is fairly dense (SG ~ 3.2) but not to the point that it concentrates readily in placer deposits. -A hardness of 7-7.5 and lack of pronounced cleavage planes makes the minerals of this group useable in jewellery. -Because tourmaline belongs to the hexagonal-trigonal crystal system it is anisotropic and exhibits two refractive indices, ranging from ~1.61 to 1.66. -Many specimens show strong pleochroism, and in rare cases it will fluoresce under UV light. -Tourmaline can be strongly coloured and hues include the entire spectrum of the rainbow, but opaque black is by far the most common. -Tourmaline's range of intense colours, size of crystals, and often euhedral shape make this mineral group a collector's favourite. Most mineralogists have a confessed affection for tourmaline and the Mineralogical Society of America even uses the outline of a "watermelon tourmaline" (left) in their logo (right). -Euhedral crystals are those that are well-formed, with sharp, easily recognized faces. The opposite is anhedral

How is Tourmaline Valued?

-Tourmaline is considered a semiprecious coloured gemstone and fetches less than emeralds, sapphires, and rubies. -Its variable saturation and colour make this gem hard to standardize prices for, but fine specimens of unusual colour can rival the prices of the "Big 3" (emerald, ruby, sapphire). Unless of unusual colour, tourmaline should typically be quite clean of inclusions. =Chrome tourmaline is usually valued at up to $400 USD per carat for a 1 carat stone, with stones reaching sizes of about 10 carats. "Normal" rubellite is on par with chrome tourmaline with similar restrictions to sizes and associated prices. -Fine rubellite with deep red-purple colouration or vibrancy can fetch up to ~$1000 USD per carat for stones in the 2 -10 carat range. Blue indicolite tourmaline is commonly valued in the same range as rubellite. Bi-colour and yellow tourmaline is more common and is priced normally in the $100 USD per carat range. -Paraíba tourmaline from Mozambique is about $1000 USD / carat for stones up to ~2 carats; above that size, prices jumps dramatically. -Stones up to almost 100 carats have been produced but are exceedingly rare, achieving prices in the $4000 USD / carat range. The source of the original Paraíba tourmaline is depleted, so stones verified from that location will demand a premium. These stones are the finest Cu-coloured type, and can reach values in excess of ~$15,000 USD per carat.

AMETHYST

-Variety of vitreous quartz with purple, violet, or red-purple colouration derives its name from the ancient Greek amethustos, meaning literally "not drunk", as it was believed to guard against drunkenness -Favoured by royalty because purple is considered a regal hue. -Found in most countries where granitic rock is exposed, amethyst commonly occurs in alluvial deposits and geodes. -Colouration is due to traces of iron, and sometimes colour-zoned due to twinning or preferential absorption on the rhombohedral faces. -Ancient Greeks believed that drinking wine from a cup of amethyst would make them immune to intoxication

What are Common Treatments for Tourmaline

-Tourmaline rough is often heated to bring dark stones into lighter hues or to saturate lighter stones. -Heat treatement can also enhance the neon-blue of Cu bearing Paraiba-type tourmaline. -Stabilization with epoxy is sometimes performed but much less common than with emerald. -Irradiation of cut stones is uncommonly observed with fancy pink tourmaline. An example of heat treatment of Paraiba-type tourmaline is given. -These two plots show the absorption spectra in the visible-to-near-infrared range (VIS-NIR) for two heat treatment experiments. Violet-Indigo is at shorter wavelengths while red-orange is at longer wavelengths, and the higher the line on the graph, the GREATER the absorption (ie, loss) of light. -When gemstones are heated in a reducing environment, electrons can be forced to 'relocate' within a crystal. One stone was kept as a reference and the other was heat treated. In the top plot, an unheated purplish crystal with Mn3+ and Cu2+ was heat treated, resulting in the Mn3+ reducing (gaining an electron) to Mn2+. Mn with a 2+ charge causes a small absorption in the deep violet region (~415 nm, bright blue line). Mn with a 3+ charge causes a broader absorption centered in the cyan-green region (~520 nm, purple line). Thus through heating, the unheated purple tourmaline effectively 'lost' its cyan-green region absorption, thus producing a desireable neon-blue Paraiba-type colouration. -In the lower plot, the unheated green tourmaline had only Mn3+ to start with, so no colour change related to Mn was noted, however, one can see a slight change. This is likely due to small amounts of Fe3+ changing to Fe2+. The other notable feature in this plot is the stronger absorption in the 400-450 nm region, due to a broad Mn-Ti absorption centered near 325 nm, as noted in the plots.

How is Colour 'Generated' in Gemstones?

-Traditional ways of explaining colour often use the terms idiochromatic (or "self-coloured" from an essential constituent), allochromatic (or "other-coloured" from an impurity), and pseudochromatic (or "false-coloured" from physical optics). This straight-forward simplification of more complex interactions between light and the coloured medium works well for describing the main colours observed in gem materials. An element responsible for colouration of a mineral is called a chromophore, and is typically one of the transition elements (e.g., Fe, Ti, Cu, Co, Mn...).

Unaltered Preservation

-Under exceptional conditions, organisms can be fossilized into an unaltered state. Minute creatures called diatoms belonging to the kingdom Protista have skeletons of silicon dioxide, which often remain unaltered. -Marine and lake-dwelling invertebrate animals, such as corals, mollusks, brachiopods, and bryozoans, have a calcareous skeleton or shell, which may be found fundamentally unaltered, even in rocks of great age. -Under even rarer circumstances, organic matter that was rapidly sealed from the air or the attack of other organisms can remain virtually intact for millions of years -Insects, small animals, and plant remains sealed in amber are the classic example, it has been suggested that even DNA might be recovered from some of them.

Turquoise

-Was one of the first gemstones to be mined, turquoise beads have been dated from about 5000 BC. -Hydrated phosphate of copper and aluminium, with the chemical formula CuAl6(PO4)4(OH)8·4H2O. -Varies in colour from sky-blue to green, depending on the amount of iron and copper it contains. -Crystals are rare; it usually occurs in massive or microcrystalline forms as encrustations or nodules, or in veins. -When crystals are found, they seldom exceed a fraction of an inch in length and occur as short prisms. -Malachite occurs principally in arid environments as a secondary mineral, probably derived from decomposition of apatite and copper sulfides, and deposited from circulating waters. -Some gem material of turquoise is very porous so it is covered in wax or resin to maintain its appearance or enhance its colour - this is called stabilized turquoise. -Usually cut en cabochon. Turquoise is very brittle naturally so cabochons are frequently backed with epoxy resin to strengthen them. Since turquoise is very porous, when it is worn next to the skin it absorbs body oils and can consequently change colour -Similar to lapis lazuli, turquoise has been used throughout antiquity as a valuable carving and cabochon stone. -It is a complex Cu - Al phosphate mineral and usually forms in microcrystalline masses with other accessory minerals, such as malachite, chrysocolla, and iron oxides. -Deposits of turquoise form near the surface close to Cu-bearing intrusive rocks (e.g., porphyries) as a result of surface waters percolating to depth and interacting with these Cu-rich rocks. -Some of the more famous deposits are in Egypt, Iran, and the United States although there are a number of turquoise occurrences scattered across the globe. -Egyptian turquoise deposits played an important role in ancient civilizations but have long been exhausted. -Deposits of Persian Turquoise from the Nishapur District in Iran, long considered the best in the market, are also reported to be running out. In North America, the turquoise deposits of New Mexico (e.g., Cerrillos Hills) and Arizona (Bisbee), which are associated with Cu ore deposits, have been mined by the Indians of the American Southwest and traded with Aztec tribes for many years. -There are no known turquoise occurrences in Canada. -Turquoise is graded based primarily on its colour, as well as on the texture of the material and presence of matrix. Colours range from green to blue, although an even medium sky blue is often the most prized. -Accordingly, the most sought after stones have little texture or matrix present.

Dispersion

-We described earlier how light rays that pass from one medium to another (at angles other than 90 degrees) undergo refraction and that the degree of refraction of light is dependant on its wavelength. -Recall that "white" light is a mixture of light with wavelengths across the visible range. -Thus when white light enters or leaves a material at angles other than 90 degrees, individual spectral wavelengths (colours) will be refracted by different amounts. -This is called dispersion. -Longer wavelengths (e.g., red) are refracted the least and shorter wavelengths (e.g., violet) are refracted the most. -This phenomenon of dispersion is what gives gemstones their fire. -In gemology, dispersion is calculated as the difference in the refractive index for light of the shortest and the longest wavelengths. Because we are only dealing with light in the visible range, we use the refraction indices of violet and red, 430.8 and 686.7 nm, respectively. -Gemstones with higher values of dispersion will show greater spreading, or dispersion, of colour. -Most notable of the gemstones is diamond, which has a dispersion value of 0.044. Here, the refractive index for violet light is 2.451 and for red it is 2.407. Thus, the dispersion is 2.451 - 2.407 = 0.044. However, there are many other stones with higher dispersion values, for example, demantoid garnet = 0.057 and titanite = 0.051. * Note that without total internal reflection light would be lost from the stone and therefore would not generate 'sparkle' or 'fire'.*

Reflection

-When light passing through one medium strikes another medium, part of that light is reflected (like a mirror) and the other part is refracted (like what you see through a fish tank). -Reflection obeys a simple geometrical law where the angle of incidence is equal to the angle of reflection (<i = <r).

Electron Microprobe and X-Ray Diffractometer

-When more detailed chemical information is required about a gemstone it can be studied using very sophisticated mineralogical tools that utilize X-Rays and electron beams to probe the samples. -Electron microprobes can determine precise chemical formulae of mineral specimen by interacting with individual atoms within the specimen. -X-Ray diffractometers (XRD) can determine precise crystallographic structures of specimens by interacting with the crystalline structure of a specimen. Both of these techniques are highly advanced and quite exciting to perform! -They probe the innermost portions of crystals and give insight to the existence of specific atoms and their interaction with surrounding atoms. The UBC Earth and Ocean Science Department has a high caliber team that use these techniques in a variety of applications.

Where is it mined globally?

-Within the historically producing regions of Myanmar (Burma), Sri Lanka, and Kashmir, a number of active mines have come and gone over the centuries as old sources dry up and new ones are discovered. -The rise of widespread global demand in the 19th and 20th century has pushed many other regions of the world into exploration and production. In fact, more than 50% of the world's coloured gemstone production is for sapphires and rubies. -Myanmar (Burma) is still the premier source for the world's rubies, even after more than two millennia of mining. -Thailand, Vietnam, and Cambodia also produce significant amounts of rubies, and although their original sources are becoming depleted, new ones continue to be discovered. Other regions of ruby production are Afghanistan, Madagascar, and Tanzania, while the historical (discovered prior to 1900) deposits of Greenland are poised to become a major producer from the western world. -Premium sapphires originate from Sri Lanka and Kashmir. Other important current sources of sapphire include Burma, Australia, Madagascar, Cambodia, Thailand, Tanzania, and Vietnam. One thing important to note is that *every ruby producing region will always contain sapphires, but not necessarily the other way around.* From the areas listed above, it may seem that there are many gem corundum mines. In reality, there really are only about 11 reliable regions that produce significant amounts of gem quality corundum: (Burma, Southeast Asia (Thailand/Cambodia), Vietnam, Sri Lanka, Madagascar, Kashmir, Australia, Afghanistan, Tanzania, Kenya, and Montana, USA. Many of these regions have small scale operations. This contrasts greatly with diamonds where there are hundreds of diamond-bearing pipes across the globe and dozens being actively mined.

CITRINE

-Yellowish to brownish quartz and resembles yellow topaz -Coloured by hydrous iron oxide, and is found in the same hexagonal crystals as other varieties of crystalline quartz -Natural citrine is much less common than amethyst or smoky quartz -Most citrine that is available is heat-treated amethyst, but heat-treated smoky quartz comes from some locations -As wish smoky quartz,, it is often marketed under names that confuse it with topaz, to inflate its price -Distinguished from topaz by its inferior hardness. -Occurs in localities that produce amethyst, sometimes known as a zone of citrine in amethyst, which is known as ametrine.

Be aware of the steps taken to discover diamonds in Canada after watching the 'Queen of Diamonds' video

-You look for -Indicator minerals (kimberlite, tiny diamonds) -Garnets, olivine -Going to the site and collecting a bunch of rock samples to test -You need to have investors to help you explore (big trade show in toronto, PDAC) -You need to get right to explore land, so often you will have to line up and compete with others -Gurney took flawed diamonds, stones with bits of minerals embedded in the clear rock -When gurney tested all the flawed diamonds, he found that the minerals were always the same (G10 garnet) -G10 garnet was always present when diamonds were present -If you found G10 garnets first, then you are probably close to finding a diamond -De Beers failed because they overlooked glaciers as glaciers, when they covered North America in the Ice Age, they pushed the geology around -Glaciers in the North scattered rock and minerals over hundreds of miles -Chuck Fipkey discovered Canada's first diamond mind (Ekati) -Eira thomas found the diavik mine, one of the richest diamond-bearing pipe in the world (after jwaneng) -How she found it: The drill intersected the softer kimberlite that eluted them till then -They found something in the core (-She hit a kimberlite pipe) : a nearly perfect 2 carat diamond -Diamond in the rough -Chance of finding a microscopic diamond in a core is very low but finding a diamond u could just drop in a ring, was insane -14. Where are Canadian diamonds sent after being mined? -Antwerp, Belgium diamond capital of the world 15. What sizes of diamonds are faceted in the north? -larger, high profit diamonds 19. Why would the retailer Tiffany & Co. invest in a mineral exploration Company? -They get first crack at the best diamonds, they secures supply 20.Why do Canadian diamonds have a certain 'pedigree'? -They don't come from an area where they may have supported some type of war in Africa -conflict-free

Describe the Gota de Aceite optical effect in emeralds

1. Which region of Colombia produces some of the finest emeralds of that country? -Muzo region, encompasses the Muzo mine but also the La Pita, Coscuez, and Penas Blancas mines 2. In short, what imparts the Gota de Aceite effect to the finest emeralds? -Emeralds display a roiled appearance that is reminiscent of honey or oil 3. What is the literal translation of Gota de Aceite? Drop of oil 4. How rare is this optical phenomenon in emeralds? -Very rare, typically only occurs in the finest of emeralds 5. Originally, calcite was assumed to play a role in this optical effect. How was this disproved? -Recent microscopic and microprobe studies showed other reasons -Unusual irregularities in the internal crystal structure are responsible for the roiled dispersion of light -These microscopic features are apparently the result of irregularities in the growth conditions during emerald crystallization that gave rise to both raised hexagonal terminations and geometric depressions -After their formation, these growth structures were further overgrown with emerald 6. Are the growth patterns random, or do they follow the crystal structure of beryl (emerald)? Irregularities 7. What does the term "Old Mine Emerald" refer to? Old mine is another term applied to rare and fine emeralds, but it refers to the provenance and age of the emerald. Specifically, it refers to emeralds sent by the Spanish colonies in the New World to Europe and Asia in the 16th, 17th, and 18th centuries, as well as Swat Valley and Habachtal emeralds of the same era (Schwarz and Giuliani, 2002). However, the presence of gota de aceite may wrongly inspire the owner or seller to call the stone "old mine." 8. What is required for a stone to have a 'distinct gota de aceite effect'? To be considered "distinct," the effect should be clearly visible to the naked eye as the stone is rocked back and forth. It is important to move the stone to reveal the liquid-like softening of the texture that is the hallmark of gota de aceite.

Different gem beryl varieties

Beryl --> colourless, opaque no chromophores, found in pegmatites Emerald --> green, substituting Cr+3 and V+3 for Al+3, found in Metasomatic zones Aquamarine --> light to dark blue-green formed from substituting Fe+2, Fe+3 for Al+3, and often Na+ in the channels, found in pegmatites Goshenite --> colourless, transparent, no substitutions, found in Pegmatites Morganite --> pink, substituting Mn+2 and Mn+3 for Al+3, found in Pegmatites Heliodor --> yellow/gold, substituting Fe3+ for Al3+, found in Pegmatites Red Beryl --> red, substituting Mn+3 for Al+3 (also has no H2O in the channels), found in Rhyolitic ejecta Maxixe --> dark blue, fading to pale blue, colour is from (NO3-) in the channels, found in Pegmatites The finest colours are not only the result of elements substituting into the crystal structure, but also due to some elements not substituting into the crystal structure. Emeralds of the finest quality require Cr+3, but also typically have very low to no Fe since this element has a broad absorption range that conflicts with subtle red fluorescence imparted by Cr (optional reading here and here). This means that the environment of emerald formation must have either low Fe or another mineral that crystallizes first and sequesters Fe before beryl can incorporate it into its own crystal structure. Examples of minerals that have been known to do this include pyrite (FeS) and siderite (FeCO3).

Cut, What is an "excellent/ideal" cut?

Cut: The external anatomy of a gemstone -The cut of a gemstone refers to the quality of the facets that define its proportions. -This is not to be confused with the shape of a cut gemstone (e.g., round brilliant, cushion, pear, etc.). -This C is probably the least understood, intuitive, and appreciated of the four, but *plays a very big role in the resulting optical effects of fire and brilliance*. -A poor cut (e.g., too shallow or too deep) can leave a stone dull and lacking life, whereas an excellent cut will return almost all of the light entering the stone back to your eye through the top (called the table; See figure below for terminology). -Cut can also have a significant impact on the weight of a diamond. For instance, two stones with the same face-up diameter can have totally different carat weights depending on how thick the culet or the pavilion is. In modern-cut gemstones the culet is often absent from the final shape or at least very small. -Grading cut is usually done by assessing the quality of the facets and their polish, as well as looking at the physical proportions of the stone. -The GIA ranking includes "excellent", "very good", "good", "fair", and "poor". -Stones with excellent (also known as ideal) cut will show good symmetry of facets as well as good Length to Width ratios when comparing the top-down dimensions of the table and full diameter. Other factors for cut grade include girdle diameter and angles for the crown and pavilion. -Shallow cut = bottom part too small, too wide, light will not reflect back up to table it will go out to the ground -Ideal = perf, light reflects back up -Deep= too thin and long, light wont reflect up, itll go around the bottom half and then outsise Table = top of diamond (not the whole diameter)/ the peak Crown = top half of diamond Pavillon = bottom half Cutlet = very tip of bottom (small flat part), usually absent now of very small Girdle = middle flat piece between the crown and pavillon Types of facets: Kite = kite shaped Star = perfect triangle, top of crown Upper girdle face = bent triangle near bottom Pavillon main facet = long, thin diamond with very long upper part Lower girdle facet = bent super long thin triangleish diamond

Describe the importance of electrical and thermal conductivity of diamond

Diamond shares physical characteristics for ones that apply for most minerals and gems, but has some other ones that are UNIQUE, like its thermal and electrical conductivities, two other properties along with refractive index and dispersion that are extensively used to confirm or reject an unknown material as being diamond. -Diamond has very HIGH thermal conductivity due to the covalent bonding that holds its carbon atoms together, and is three times higher than that of gold and silver, two metals known for their own high thermal conductivity. -Compared to its simulants, such as cubic zirconia or quartz, diamond's thermal conduction is a lot higher -Some simulants, like moissanite, which have similar thermal conductivities and so additional properties are required to be tested -The electrical conductivity of a diamond is not remarkable per se, however, its low electrical conductance paired with high thermal conductance is unusual. -Consequently, these properties together can also be distinctive from other materials, such as moissanite. -Diamond itself is an insulator (High resistivity) whereas some of its simulants, such as moissanite, are semiconductors and will more readily pass electricity when an electrical charge is placed across the stone in question.

How is a Diamond Recognized and Distinguished from Other Materials?

First obvious test: Hardness, since no other mineral will scratch diamond. The problem with this technique, however, is that something needs to be scratched. Ideally, non-destructive tests should be used. Most commonly used by professional gemologists: Is thermal conductivity. Diamond testers have been developed to measure this feature for stones mounted in jewellery. Second: Electrical conductivity is used to discern diamond from other high thermal conductivity materials like moissanite Other properties: Refractive index, dispersion, isometric/cubic optic nature. -Diamonds also repels water and sticks slightly to grease - a property exploited in processing diamond ore -Some diamonds will fluoresce under UV light but testing for this property only reveals information 'about' diamond, not whether the material tested 'is' a diamond. -Materials commonly used to imitate diamond (and their diagnostic properties relative to that of diamond are moissanite (greater dispersion, greater refractive indices, not isometric, more electrical conductivity), cubic zirconia (lower thermal conductivity), glass (lower thermal conductivity), strontium titanite (lower thermal conductivity) and yttrium-aluminum-garnet (lower thermal conductivity). Thermal conductivity is the best property to test for since it rules out many possible imitations. -In recent years the marketplace has started to see application of nanocrystalline diamond onto the surface of various gems and imitation material in order to modify colour and improve durability which is causing problems in identification and characterization of gem materials.

Cullinan Diamond

For many years, the great diamond was a symbol of the world's mightiest empire. - At 3,106 ct, today it remains the largest gem diamond ever discovered, and two of the diamonds cut from it lie at the heart of the Crown Jewels of England -Discovered around 1905 from Premier Mine -Premier mine significant because in its 100+ years of operation, has yielded more rough diamonds over 100 ct (300+) than any other single source, including more than 25% of all the 400+ ct diamonds ever discovered What was the first step taken by Asscher in transforming the rough stone into a gem? saw two visible inclusion, split the diamond into two What is the purpose of Figures 12 and 16, the plotting diagrams? shows quslity of the stone What are the physical dimensions of the Cullinan II, and how many facets does it have? 33 crown and 33 pavillion facet It measures 45.4 x 40.8 x 24.2 mm and weighs 317.40 ct What type of information do you think that Infrared and UV-Visible spectroscopy revealed to the gemologists and what did they infer from the results? type 2 diamond

GIA ranking of clarity

GIA definitions for clarity grading: Flawless (FL): no blemishes or inclusions when examined by a skilled grader under 10X magnification. Internally Flawless (IF): no inclusions when examined by a skilled grader, and only insignificant blemishes under 10X. Very Very Slightly Included (VVS1 > VVS2): contains minute inclusions that are difficult for even a skilled grader to locate under 10X. VVS1: extremely difficult to see, visible only from the pavilion or small and shallow enough to be removed by minor repolishing. VVS2: very difficult to see. Very Slightly Included (VS1 > VS2): contains minor inclusions ranging from difficult (VS1) to somewhat easy (VS2) for a trained grader to see under 10X. Slightly Included (SI1 > SI2): contains noticeable inclusions which are easy (SI1) or very easy (SI2) to see under 10X. In some SIs, inclusions can be seen with the unaided eye. Included (I1 > I2 > I3): contains inclusions which are obvious to a trained grader under 10X, can often be easily seen face-up with the unaided eye, seriously affects the stone's potential durability, or are so numerous that they affect transparency and brilliance. To the consumer, inclusions tend to be viewed in a negative light. However, to gemologists and geoscientists, these inclusions can hold a wealth of information. Solid and fluid inclusions can provide information on the formation of diamonds in their stability zone and allude to their growing conditions. These inclusions can also provide evidence of the original source of the stone or proof that it is not synthetic or has not undergone certain treatments. A recent block of text from a scientific session regarding solid inclusions in minerals describes this well: Inclusions of minerals trapped within other mineral grains provide a sensitive record of the conditions and microenvironment in which the host mineral grew. Understanding how this environment varied during growth is crucial for developing tectonic models, identifying chemical disequilibrium, unraveling igneous processes, and deciphering crust and mantle dynamics. The application of high-resolution spectroscopic methods to mineral inclusions in igneous and metamorphic rocks, allows interrogation of geologic processes from the shallow crust to the deep mantle.

HPHT vs LPHT annealing

HPHT annealing is by far the most common colour treatment for diamonds. -By employing this technique, technicians are able to increase the temperature of a diamond while maintaining a very high pressure, and preventing graphitization (conversion of diamond to graphite) of the stone -This has profound effects on the crystal structure with the ability to alter the combination states of nitrogen impurities (changing from Type Ia to Ib and vice versa) and "heal" lattice vacancies -Depending on the starting type of diamond and the exact temperatures and pressures used, a lot of different colours could be produced -Most common result of this method is removing a brown body colour; and removing or enhancing an existing yellow colour. -Other colours such as blue, green, pink, and yellow can be produced indirectly after the dominant brown colour is removed and other colour centres are no longer obscured. -LPHT annealing is similar to HPHT, except that graphitization of the diamond is encouraged at low pressures -This is often the procedure chosen for highly-flawed stones with numerous inclusions or fractures which are considered ugly and thus, not valuable -By increasing temperature at low pressures, the crystal structure of diamond starts to change to graphite along fracture surfaces -This produces an overall black/dark appearance to the stone, hiding all impurities Combinations of all three colour treatments are possible with HPHT and irradiation being the most common pairing. This gives researchers and technicians to produce virtually the entire colour spectrum of diamond depending on the starting stone type and existing colour centres.

Colourless Diamonds reasons

IIa, pure Best achievable is 'D' colour, theses stones command premium prices

Lapis Lazuli

Lazurite → Main component of lapis lazuli and accounts for the stone's intense blue colour, although lapis lazuli also contains pyrite and calcite and usually some sodalite and hauyne too. -Lazurite itself, is a sodium calcium aluminosilicate sulfate and forms distinct crystals, but is not the same as phosphate lazulite. In lapis lazuli, lazurite is well dispersed. -Best quality lapis lazuli is intense dark blue, with minor patches of white calcite and brassy yellow pyrite. -Lapis lazuli is relatively rare and commonly forms in crystalline limestones (metamorphosed rocks) as a product of contact metamorphism. Mines in Afghanistan are a major source. -Lapis lazuli is actually not a single mineral, but rather a mixture comprising mostly of lazurite, pyrite, and calcite with minor diopside, sodalite and haüyne. -Of those, the blue colouration comes from lazurite, sodalite and hauyne, although the two latter minerals are not ALWAYS blue in colour. Lapis lazuli has a long history dating back to the Egyptian and Babylonian civilizations and in historical Europe was often called "ultramarine". -Today, most lapis lazuli is produced from Sar-e-Sang, Afghanistan, with minor production in the Lake Baikal region of Russia and the Andes in Chile near Coquimbo. -Canada hosts one known lapis lazuli deposit, and it is located in the far north of Baffin Island. -The USA has two main localities: one at Italian Mountain in Colorado and the other near Balmat, New York.

More about Olivine

Many people may not familiar with olivine, but the gem name peridot is as common as a neighborhood cat. The word "peridot" is likely derived from the Arabic word for gem, "faridat". -Historically, the best gem peridot comes from St. John's Island in the Red Sea (once called Topazios, now called Zabargad) where mining of this gem stretches back over 3,500 years. -One locality of note is a Hawaiian beach that is comprised almost entirely of olivine named Papakolea Beach, but is locally referred to as the "Green Sand Beach". Large stones like those from Zabargad, however, are quite rare and most finished peridot is less than 3 carats. -The largest cut fine peridot gem weighs just over 300 carats and today sits at the National Museum of Natural History. Important localities of peridot today include the USA (Arizona), Pakistan (Sapat Valley) and Burma/Myanmar, but many other localities also provide gem rough (e.g, New Mexico, Italy, Zimbabwe, China, Russia, Brazil, Kenya, Mexico, New Caledonia, etc...). -In BC, peridot has been noted near Atlin, Dease Lake, Timothy Mountain (Lac la Hache), Big Timothy Mountain (near Hendrix Lake), Prince George area, andLightning Peak (near Cherryville). -Olivine itself is actually a mineral group comprising two main solid solution endmembers, forsterite (Mg2SiO4) and fayalite (Fe2SiO4). You might recognize those names and formulae from Lessons 7 and 12! The gem variety of olivine, peridot, is almost always the mineral forsterite with a predominance of Mg over Fe. -This is because with increasing amounts of Fe there is an increasing amount of absorbtion, rending the crystals quite dark. The crystallographic site of Fe and Mg in the olivine group also permits other trace elements to enter the structure, such as Ni, V, Cr, and Mn. -Peridot occurs prolifically in rocks called peridotite (see page 40 in your text) that form in the "Upper Mantle" and are occasionally brought to the surface as nodules in eruptive basalts as xenoliths, often alkali basalts (not unlike those that bring xenocrystic corundum to the surface!). -Peridot is also commonly found in a subclass of peridotite called dunite, which by definition is composed of greater than 90% olivine. In order to force dunite from the upper mantle to the surface a special process called obduction is required where deep seated oceanic crust and upper mantle rocks are overthrust on top of (usually) continental crust. -Normal subduction between these rock types is characterized by the denser oceanic crust being forced underneath the more 'buoyant' continental crust. When a set of rocks have been obducted the entire package is often termed "ophiolite" and provide excellent locations (e.g., Oman and Cyprus) for scientific study of geological processes that would otherwise be unobservable! -Because peridotite rocks formed in the Upper Mantle under higher pressures and temperatures, and because the rocks contain a large amount of reduced iron (2+ state), they readily undergo alteration at the Earth's surface. -This particular process of alteration affecting peridotites (one set of minerals converting to another set of minerals, often facilitated by percolating water) is called serpentinization and results in a large amount of the 'new' mineral serpentine (page 256 in your text), sometimes replacing the original rock completely. -Another interesting type of peridot is called "Pallisitic Peridot", as it originates from a class of meteorites called pallisite; it is, therefore, an extraterrestrial gemstone! In this case, olivine is hosted in these rare types of stony iron-nickel meteorites, the only kind with crystals large enough to turn into gemstones. It has been postulated that pallasites were likely formed during violent events that mixed mantle and core materials, probably from asteroids but possibly from planetary sources. Less than 100 of these meteorites are known. The gem olivine from pallasite meteorites is typically yellowish-green as compared to 'terrestrial' peridot but otherwise shares many of the same properties. One distinction, though, is the trace element composition of pallasite-peridot as compared to terrestrial stones. -Using Laser Ablation ICPMS methods, Shen et al (2011) found that the extraterrestrial peridot was higher in V and Mn, while being distinctly lower in Li, Ni, Co and Zn.

More modern colour treatments

Modern Diamond treatments -HPHT annealing (High pressure, High temperature), LPHT annealing (Low pressure, High temperature) and Irradiation, with HPHT annealing being the most important and prominently used process -Irradiation techniques create VACANCIES within the atomic lattice of diamond, which generate colour centers that can absorb light in the visible and near infrared portions of the electromagnetic spectrum -These treatments of diamonds were first employed around the turn of the 20th century and the process generally involved exposure of stones to the element radium, which imparted a bluish-green colouration in the stone. -This usually took several months of exposure to achieve and the colour would be limited only to a very thin outer layer of the stone (along with residual radioactivity in the diamond that could last for hundreds of years) -With the advent of NEUTRON RADIATION, the defects (and therefore colour) were able to be imparted throughout the entire stone and leave no detectable radiation -Green-coloured diamonds can also be produced naturally if the stones are situated in proximity to certain minerals which emit natural radiation

General Type I and Type II stats (which one is most common, which is least common) (what colours each produces)

Most diamonds (~98%) belong to the Type Ia group, those containing appreciable amounts of N that are clustered in the crystal structure. -Type Ia diamonds exhibit absorption of blue light and therefore show an overall yellow hue. -Type IIa is the next most common type of diamond (<2%). -These diamonds have no appreciable N or B substituting for carbon in the structure. -Due to a lack of impurities, these diamonds tend to show the whitest colour with little to *no absorption of light across the visible spectrum*. -*Physical deformation and resulting crystal defects* in Type IIa crystals give rise to most *pink*, purple, and brown diamonds. -Type IIb diamonds are very rare and contain minute amounts of B in the crystal structure but no appreciable N -Optically, the incorporation of boron causes most light except blue to be absorbed, impairing a blue to grey hue. -These diamonds are v rare and include specimens like the *Hope Diamond* -Type Ib diamonds are also very rare and characterized by appreciable N, but scattered about the crystal lattice. Diamonds of this type occur in a range in colours including yellow, brown, orange, and green or can be colourless.

Nephrite

Nephrite → One of the two different minerals known as jade. -More common and widespread than jadeite. Not a mineral name, but the name is applied to the tough, compact form of either the amphibole tremolite or actinolite. -Both are calcium magnesium silicate hydroxides, and are structurally identical, except that in actinolite some of the magnesium is replaced by iron. -Nephrite is composed of a mat of tightly interlocking fibers, creating a stone tougher than steel. -Where nephrite is found, especially in China and New Zealand, this toughness brought it into use very early on for tools and weapons. The colour is dark green when iron-rich; cream-coloured when magnesium-rich. -Nephrite is formed in metamorphic environments, especially in metamorphosed ultramafic rocks where it is associated with talc and serpentine, and in regionally metamorphosed areas where dolomites have been intruded by mafic rocks.

Other treatments (non colour)

Other treatments: -Treatments that are not aimed towards colour are also used on diamonds and other gems -Used to treat the stone's clarity Glass-filling, Laser-drilling, and Acid Boiling Glass filling → used to fill in surface-reaching fractures and flaws which greatly improves the overall clarity of the stone. The glass used needs to be of an appropriate refractive index in order to reduce the visibility of a fracture within diamond, which has a refractive index of 2.435 In modern treatments, lead-bismuthate glass is usually used which has a refractive index greater than 2 depending on its composition Laser-drilling → Involves using a very high powered laser to drill into the diamond to reach inclusions that are otherwise sealed from the surface of the stone. Once an inclusion is reached, the diamond is put in a boiling acid bath which either bleaches or dissolves out the inclusion. The resulting pit and drill hole are then filled in with glass. These three techniques are commonly used in combination with each other. The main objective of treating gemstones is to hide or remove imperfections or undesirable features, so it is important for merchants to list all the treatments that have been applied. Failure to do so could deceive buyers and result in damaging the stone if another treatment is applied (e.g. HPHT on a diamond with glass fillings).

Blue Nile

Pricing of diamonds can be made available directly to consumers through jewellery shops and online retailers. A company called Blue Nile has been selling diamonds online since the late 1990's directly to consumers. They offer a very large range of stones, all of which are listed with their prices. eBay is also a "good" resource for consumers to check-out what diamonds (and coloured gemstones) can fetch, however, there is no control or moderation for those auctions.

Secondary accumulation in placers

Secondary deposits of sapphires are a major source of gem material. Corundum in these environments formed in some sort of primary setting (e.g., marble or alkali basalt) and has concentrated in a more spatially restricted environment through the processes of weathering and erosion. Because corundum has a higher specific gravity than most minerals, it will tend to settle to the base of alluvial systems, similar to how gold concentrates in placer deposits. The natural process of weathering effectively "enriches" occurrences of sapphire by concentrating material as well as by breaking any crystals that were weak to begin with. The end product is a well sorted collection of crystals typically of high quality. -These crystals are also often rounded and abraded from their time during transport. The greater the rounding, the greater the distance from their original source. It is worthwhile to quickly compare the morphology of the rounded grains in the images below to those crystals in the previous two pages to see the full difference. -Important global secondary deposits exist in eastern Africa, Australia, Madagascar, Myanmar, Sri Lanka, and Tanzania - all areas with warm climates and relatively high rates of weathering. Of course, any area with a primary occurrence of gem corundum will also have the potential for secondary deposits no matter how slow the weathering rates, and sometimes a single placer will have gemstones from multiple sources. Other gem minerals can also be found in these secondary placer deposits including zircon, painite, tourmaline, beryl, and diamond.

Light of the desert video

The Light of the Desert - Video by Royal Ontario Museum This 3 minute video describes a wonderful ~900 carat gem (cerussite, a lead carbonate) on display at the Royal Ontario Museum in Ottawa, Ontario. Use the following questions to help you through the video: 1. Why would this gem be difficult to facet? -Because there is heat generated through the grinding, cutting, and polishing. -Typically, cerussite shatters when you are trying to cut it -The maximize size you could cut with cerussite is around 200 carats. -a 900 carat gem would have been really hard to cut -Even heat from a palm could shatter the gem 2. How much does this 900 carat gem weigh in grams? 180 grams 3. What physical property gives a gem its fire? -The resulting dispersion that the stone displays, produced through a combination of natural optics existing in the gem and style of cut the cutter uses 4. Why might the physical size of a gem have an impact on the resulting fire? -It may be hard for a cutter to cut a large gem -The larger a diamond is, the more natural optics it has which leads to more fire 5. What is a 'pavilion'? What is its function? -The bottom half of a gem, it is designed to take the light and reflect it back up into your face and gives the gem its sparkle -There are some gems that not only are able to reflect it back to the viewer but can also split the light into its spectral colours (dispersion, or fire of the gem)

Subtractive Colour Theory

The colour of a gemstone in balanced white light is largely the result of absorption and transmission of certain wavelengths of electromagnetic radiation by the gemstone. The colour that we see (wavelengths that are transmitted through the gem and/or reflected from its surface) are complimentary to the colours (wavelengths) that are absorbed in subtractive colour theory. In a sense, gemstones are like "colour filters". --The absorption qualities of a material will usually define how it looks to our eye after light has interacted with it. For example, if 'white' light is shined on a surface that appears red to our eyes, then that means electromagnetic radiation in the 'red region' is most effectively reflected. -If all wavelengths of visible spectrum is shined on black object, it appears black -An example is if blue-violet light is absorbed, the resulting wavelengths that are transmitted will produce yellow colour, as interpreted by our eyes. If all wavelengths other than blue and red are absorbed (ie, blue and red transmitted, green absorbed), we would see purple/magenta. It is important to remember that when we 'absorb' a particular colour we are absorbing swaths of the electromagnetic spectrum in bell-curved shapes, not single-line wavelengths.

Describe the primary morphology of diamonds, and the determining factors of the morphology

The external shape (habit) of any mineral is controlled by its internal arrangement of atoms. -Carbon atoms in diamond have cubic symmetry, so the primary shapes that diamond can take must adhere to the rules dictated by this symmetry -Secondary, or modifying, shapes can change the initial shape of any mineral through processes like corrosion or abrasion -Resulting shape of natural uncut diamonds is a mixture of primary crystallographically controlled shapes variably modified by secondary processes. -Certain morphologies can indicate specific growth environments and subsequent geological history of a particular set of diamonds. -*Most common habit/shape of diamond* is the octahedron. -Cubes are also common shapes, as well as combos of cubes and octahedrons (octahedron modified by cube faces, or cubes modified by octahedron faces). -Uncommonly, diamonds can be dodecahedral, twinned or show a flat tabular form known as macles -Diamonds sometimes form in polycrystalline aggregates and tend to be harder than monocrystalline specimens -Longer arrows on a diagram mean a harder plane, so harder to erode but better for polishing -The cube faces are the easiest to polish and the tables of cut diamonds are usually parallel with this plane. -Temperature at which a diamond grows = a strong determining factor on diamond morphology, with *higher temperatures yielding octahedral shapes* -The shape of diamonds is also affected by the saturation conditions diamond grows in. -Under supersaturated conditions (being more highly concentration ins solution than normally possible) diamond grows too fast resulting in cloudy crystals or fibre-like overgrowths

Topaz, Tourmaline, and Spodumene

The word tourmaline has its roots in the Sinhalese word turamali which roughly translates to "stone with many colours". This gemstone is known for not only for its diverse colour range, but also its diverse colour range in single crystals! It also possesses many of the other important features of a gemstone, including transparency, rarity, durability and hardness. Topaz has been known throughout antiquity, however, it is thought that this word was applied to a variety of gemstones such as peridot, aquamarine, or citrine. Its name likely comes from the island of Zabargad, formerly called Topazos. Interestingly, Zabargad is a classic source for gem quality peridot not topaz. Both the names of spodumene's gem varieties, kunzite (pink) and hiddenite (green), originate from individuals. A.E. Hidden recognized gem quality green spodumene in North Carolina at the end of the 19th century and G.F. Kunz was a famous American mineralogist who was lucky enough to have a gem named after him!

Transparency

Transparency describes how light transmits through a medium. There are roughly five main groups, 1) transparent 2)semi-transparent 3) translucent 4) semi-translucent 5) opaque. 1) Transparent minerals are those where objects can be viewed through the medium (e.g., glass, diamond, beryl). 2)Semi-transparent minerals are those where objects can be viewed through the medium, but object are heavily blurred (e.g., chalcedony, moonstone). 3)Translucent minerals are those where objects cannot be viewed through the medium, although light will pass through the medium with lesser intensity (e.g., jade, opal, agate). 4)Semi-translucent minerals are those where objects cannot be viewed through the medium and light will only pass through the medium if it is thin (e.g., jade, turquoise). 5)Opaque minerals are those where objects cannot be viewed through the medium, and no light will pass through (e.g., pyrite, malachite, galena).

What is Topaz and What are its Basic Qualities?

True topaz is an aluminosilicate mineral containing fluorine (F); often, appreciable hydroxyl groups (OH)- replace F. -It is part of the orthorhombic crystal system and usually forms prismatic crystals with an eight sided cross-section (similar in shape to a lozenge) that are terminated in a wedge-like fashion. -Striations are common along the length of the crystal. A perfect basal cleavage makes this mineral difficult to work with in jewellery, however, it has a good hardness of 8, placing it above quartz and tourmaline but below corundum on the Mohs scale. -It is fairly dense with a SG of ~3.5. -Topaz crystals can reach considerable sizes and single crystals up to 10 m long and 3 m across have been found, weighing up to ~350 tonnes! Of course, these crystals would not be of gem quality. -Gemmy ones have been found up to several hundred kilograms. These make for particularly large cut stones, often in the thousands of carats! The largest cut topaz is from Ouro Preto, Brazil, weighs 22,892.5 carats and is hosted in the Smithsonian Institution National Museum of Natural History. Although from Brazil, it boasts the name "American Golden Topaz".

Type II

Type II diamonds have N less than 10 ppm (considered to be Nitrogen-free) -Type II diamonds with little to no N in their crystal structure can be subdivided into: Type IIa → boron free, whitest colour Type IIb → contain minute amounts of B, up to about 10 ppm

Type Ia further divisions

Type Ia diamonds with clustered N are subdivided into: most common, yellowish Type IaA with paired N atoms Type IaB where 4 N atoms (quads) are clustered often with a vacancy (absence of atoms) at their center

Pink, purple, red, cognac:

Usually Ia, colour likely from deformation of crystal structure, Rob Red and Agra Diamonds

Wave parts

crest -- highest point of a wave trough -- lowest point of a wave wavelength (λ) -- distance between two successive crests or two successive troughs of a wave (nanometres or 10^-9 metres, nm) frequency (f) -- number of waves passing a point per unit of time (cycles per second or hertz, Hz) velocity (v) -- velocity (or speed) of the wave and in this case it is the speed of light, which in a vaccuum is 3.0x10^8 m/s (meters per second, m/s) amplitude A ---vertical distance between crest or trough and the equilibrium line (nanometres or 10-9 metres, nm) wavelength = v/f

Green

natural irradiation The Dresden Green (a Type IIa diamond too