Rocks and Minerals: Silicate Family

Aventurine

a form of quartz, characterised by its translucency and the presence of platy mineral inclusions that give it a shimmering or glistening effect termed aventurescence. Family: Silicate Formula: SiO2 Color: Usually green. Also orange, yellow, red, pink, purple, white, brown, and blue. Habit: Crystal system: hexagonal Streak: colorless Luster: vitreous, aventuresecnt Cleavage: Fracture: Tenacity: Hardness: 6.5-7 SG: 2.6-2.7 Diaphaneity: Formation: Other: most common color of aventurine is green, but it may also be orange, brown, yellow, blue, or grey. Chrome-bearing fuchsite (a variety of muscovite mica) is the classic inclusion and gives a silvery green or blue sheen. Oranges and browns are attributed to hematite or goethite Green aventurine is a common material used to produce beads and cabochons. These are used to make earrings, pendants, rings, and other jewelry. Aventurine and translucent quartz without aventurescence are often dyed bright colors. Dye is used to produce low-cost cabochons with bright colors that are often seen in inexpensive jewelry.

Beryl

a minor ore of beryllium, and color varieties of the mineral are among the world's most popular gemstones. Emerald, aquamarine, heliodor, and morganite are the most popular varieties Family: Silicate Formula: Be3Al2Si6O18 Color: Green, yellow, blue, red, pink, orange, colorless Habit: Crystal system: Hexagonal Streak: colorlesss Luster: vitreous Cleavage: imperfect Fracture: Tenacity: Hardness: 7.5-8 SG: 2.6-2.8 Diaphaneity: transparent to translucent Formation: contains a significant amount of beryllium. Beryllium is a very rare metal, and that limits the formation of beryl to a few geological situations where beryllium is present in sufficient amounts to form minerals. It mainly occurs in granite, rhyolite, and granite pegmatites; in metamorphic rocks associated with pegmatites; and, in veins and cavities where hydrothermal activity has altered rocks of granitic composition. These different types of deposits are often found together and serve as an exploration indicator for finding beryl. Beryl is also found where carbonaceous shale, limestone, and marble have been acted upon by regional metamorphism. The famous emerald deposits of Colombia and Zambia were formed under these conditions. The carbonaceous material is thought to provide the chromium or vanadium needed to color the emerald. Other: Beryl once served as the world's only important ore of beryllium metal. But in 1969, Spor Mountain, Utah became the source for about 80% of the world's beryllium supply when bertrandite, a beryllium silicate hydroxide mineral, was discovered there. The extraction of beryllium from beryl is very costly, and as long as bertrandite is available in large amounts, beryl will remain a minor ore of that metal. Small amounts of beryl, mostly produced as a by-product of gemstone mining, are still used to produce beryllium. The most important use of beryl today is as a gemstone. It is one of the most important gem minerals, and the gems of beryl are named by their color as: emerald (green), aquamarine (greenish blue to blue), morganite (pink to orange), red beryl (red), heliodor (yellow to greenish yellow), maxixe (deep blue), goshenite (colorless), and green beryl (light green). Synthetic beryl has been commercially manufactured for gemstone use since the 1930s. Synthetic beryls have the same chemical composition and physical properties as natural beryl. They can be fashioned into gemstones that rival the beauty of natural gems and can be sold for a much lower cost. Many people opt for a synthetic emerald because it can have a superior color, superior clarity, greater durability, and a much lower cost than a natural gem.

Agate

Agate is one of the most common materials used in the art of hardstone carving, and has been recovered at a number of ancient sites, Family: Silicate Formula: SiO2 Color: brown, white, red, gray, pink, black, and yellow. The colors are caused by impurities and occur as alternating bands within the agate. The different colors were produced as groundwaters of different compositions seeped into the cavity. The banding within a cavity is a record of water chemistry change. This banding gives many agates the interesting colors and patterns that make it a popular gemstone Habit: Crystal system: Streak: white Luster: waxy, dull Cleavage: none Fracture: conchoidal, subschoncoidal Tenacity: brittle Hardness: 6.5-7 SG: 2.6 Diaphaneity: Formation: generally forms by the deposition of silica from groundwater in the cavities of igneous rocks. The agate deposits in concentric layers around the walls of the cavity, or in horizontal layers building up from the bottom of the cavity. These structures produce the banded patterns that are characteristic of many agates. Some of these cavities are lined with crystals and those are known as geodes. Other: Lace agate is a variety that exhibits a lace-like pattern with forms such as eyes, swirls, bands or zigzags. Moss agate, as the name suggests, exhibits a moss-like pattern and is of a greenish colour. The coloration is not created by any vegetative growth, but rather through the mixture of chalcedony and oxidized iron hornblende. Dendritic agate also displays vegetative features, including fern-like patterns formed due to the presence of manganese and iron oxides.[14] Turritella agate (Elimia tenera) is formed from the shells of fossilized freshwater Turritellas, gastropods with elongated spiral shells. Similarly, coral, petrified wood, porous rocks and other organic remains can also form agate.[15] Coldwater agates, such as the Lake Michigan cloud agate, did not form under volcanic processes, but instead formed within the limestone and dolomite strata of marine origin. Like volcanic-origin agates, Coldwater agates formed from silica gels that lined pockets and seams within the bedrock. These agates are typically less colorful, with banded lines of grey and white chalcedony.[16] Greek agate is a name given to pale white to tan colored agate found in Sicily, once a Greek colony, back to[clarification needed] 400 BC. The Greeks used it for making jewelry and beads. Brazilian agate is found as sizable geodes of layered nodules. These occur in brownish tones inter-layered with white and gray. Quartz forms within these nodules, creating a striking specimen when cut opposite the layered growth axis. It is often dyed in various colors for ornamental purposes. Polyhedroid agate forms in a flat-sided shape similar to a polyhedron. When sliced, it often shows a characteristic layering of concentric polygons. It has been suggested that growth is not crystallographically controlled but is due to the filling-in of spaces between pre-existing crystals which have since dissolved.

Apophyllite

a specific group of phyllosilicates, a class of minerals. includes the members fluorapophyllite-(K), fluorapophyllite-(Na), hydroxyapophyllite-(K). derived from the Greek apophylliso, meaning "it flakes off", a reference to this class's tendency to flake apart when heated, due to water loss. Exfoliation of apophyllite is also possible by treating it with acids or simply by rubbing it. Family: Silicate Formula: (K,Na)Ca4Si8O20(F,OH)·8H2O Color: Usually white, colorless; also blue, green, brown, yellow, pink, violet Habit: Prismatic, tabular, massive Crystal system: P4/mnc (no. 128) Streak: white Luster: vitreous; pearly Cleavage: Fracture: uneven Tenacity: Hardness: 4.5 - 5 SG: 2.3 - 2.4 Diaphaneity: transparent to translucent Formation: typically found as secondary minerals in vesicles in basalt or other volcanic rocks. Other: Whereas most phyllosilicates have a T layer (silica backbone) consisting of interlocked 6-fold rings of silica tetrahedra, with pseudohexagonal symmetry, the T layer in apophyllite consists of interlocked 4-fold and 8-fold rings of silica tetrahedra with true tetragonal symmetry

Citrine

a transparent variety of quartz with a yellow to orange color. Its attractive color, high clarity, low price, and durability make it the most frequently purchased yellow to orange gem. Family: Silicate Formula: SiO2 Color: pale yellow to brown Habit: 6-sided prism ending in 6-sided pyramid (typical), drusy, fine-grained to microcrystalline, massive Crystal system: Streak: white Luster: vitreous Cleavage: Fracture: conchoidal Tenacity: Hardness: 7 SG: 2.65 Diaphaneity: translucent Formation: Color due to a submicroscopic distribution of colloidal ferric hydroxide impurities Other: Reddish orange and reddish brown are rare colors in quartz. Gems of these reddish colors are often called Madeira citrine. Citrine and topaz are both available in the yellow to orange color range, but citrine generally has a much lower cost. 1. citrine with a natural color2. citrine with a natural color, but enhanced by treatment3. citrine produced by heating light amethyst4. synthetic citrine (a man-made product)5. imitation citrine (a man-made product that is not SiO2)

Actinolite

Derived from the Greek word aktis (ἀκτίς), meaning "beam" or "ray", because of the mineral's fibrous nature. intermediate member in a solid-solution series between magnesium-rich tremolite and iron rich ferro actinolite. Family: Silicate Formula: Ca2(Mg4.5-2.5Fe2+0.5-2.5)Si8O22(OH)2 Color: pale to dark green, yellowish green and black. White or grey when in asbestos Habit: bladed, fibrous, radial Crystal system: monoclinic Streak: white Luster: vitreous to dull Cleavage: perfect along one axis Fracture: uneven Tenacity: Hardness: 5-6 SG: 3 Diaphaneity: translucent to transparent Formation: commonly found in metamorphic rocks, such as contact aureoles surrounding cooled intrusive igneous rocks. It also occurs as a product of metamorphism of magnesium-rich limestones Other: Some forms of actinolite are used as gemstones. One is nephrite, one of the two types of jade

Almandine

Family: Silicate Formula: Color: Habit: Crystal system: Streak: Luster: Cleavage: Fracture: Tenacity: Hardness: SG: Diaphaneity: Formation: Other:

Augite

Family: Silicate Formula: Color: Habit: Crystal system: Streak: Luster: Cleavage: Fracture: Tenacity: Hardness: SG: Diaphaneity: Formation: Other:

Rhodonite

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Sodalite

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Spodumene

Family: Silicate Formula: Color: Habit: Crystal system: Streak: Luster: Cleavage: Fracture: Tenacity: Hardness: SG: Diaphaneity: Formation: Other:

Staurolite

Family: Silicate Formula: Color: Habit: Crystal system: Streak: Luster: Cleavage: Fracture: Tenacity: Hardness: SG: Diaphaneity: Formation: Other:

Stilbite

Family: Silicate Formula: Color: Habit: Crystal system: Streak: Luster: Cleavage: Fracture: Tenacity: Hardness: SG: Diaphaneity: Formation: Other:

Willemite

Family: Silicate Formula: Color: Habit: Crystal system: Streak: Luster: Cleavage: Fracture: Tenacity: Hardness: SG: Diaphaneity: Formation: Other:

Zircon

Family: Silicate Formula: Color: Habit: Crystal system: Streak: Luster: Cleavage: Fracture: Tenacity: Hardness: SG: Diaphaneity: Formation: Other:

Kyanite

Family: Silicate Formula: Al2SiO5 Color: Blue, white, gray, green, colorless Habit: bladed Crystal system: triclinic Streak: white, colorless Luster: vitreous, pearly Cleavage: Perfect in two directions, faces sometimes striated Fracture: Tenacity: Hardness: 4.5 -5 along the length, 6.5-7 along the width SG: 3.5-3.7 Diaphaneity: transparent to translucent Formation: Other: Kyanite is used to manufacture a wide range of products. An important use is in the manufacture of refractory products such as the bricks, mortars, and kiln furniture used in high-temperature furnaces. For foundries, the molds that are used for casting high-temperature metals are often made with kyanite. Kyanite is also in products used in the automotive and railroad industries where heat resistance is important. Mullite, a form of calcined kyanite, is used to make brake shoes and clutch facings. well suited for the manufacture of a high-refractory-strength porcelain - a porcelain that holds its strength at very high temperatures. A familiar use of this type of porcelain is the white porcelain insulator on a spark plug. Kyanite is also used in some of the more common forms of porcelain, such as those used to make dentures, sinks, and bathroom fixtures Kyanite's heat resistance and hardness make it an excellent material for use in the manufacture of grinding wheels and cutting wheels. It is not used as the primary abrasive; instead, it is used as part of the binding agent that holds the abrasive particles together in the shape of a wheel. Kyanite, unlike most other minerals, can expand significantly when heated.

Epidote

Family: Silicate Formula: Ca2(Al2,Fe)(SiO4)(Si2O7)O(OH) Color: Usually yellowish green to pistachio green, sometimes brownish green to black Habit: Crystal system: Streak: Colorless Luster: vitreous to resinous Cleavage: perfect in one direction, imperfect Fracture: Tenacity: Hardness: 6-7 SG: 3.3-3.5 Diaphaneity: transparent to translucent to nearly opaque Formation: commonly found in regionally metamorphosed rocks of low-to-moderate grade. In these rocks, epidote is often associated with amphiboles, feldspars, quartz, and chlorite. It occurs as replacements of mineral grains that have been altered by metamorphism. It is frequently found in veins that cut granite. It occurs as monoclinic crystals in pegmatites. It is also found in massive form and as monoclinic crystals in marbles and schists that were formed or altered through contact metamorphism. Other: an end member of a solid solution series with clinozoisite. In that series, the iron of epidote is gradually replaced by aluminum to the end member clinozoisite composition of Ca2Al3(SiO4)(Si2O7)O(OH). Clinozoisite is usually lighter in color than epidote because iron is what produces epidote's greenish to brownish color. Epidote is a rock-forming mineral. Many regionally metamorphosed rocks contain small amounts of epidote. Two rock types that contain significant amounts of epidote are epidosite and unakite. Locations where these rocks can be found are rare, but at those locations significant amounts of these rocks can be present. Epidosite is a metamorphic rock composed mainly of epidote with small amounts of quartz. It forms when basalts in sheeted dikes and ophiolites are transformed by hydrothermal activity or metasomatism. Unakite is a rock that forms from the metamorphism of granite. Less-resistant minerals in the granite are altered to epidote or replaced by epidote, with the orthoclase and quartz remaining. It is an interesting pink and green colored rock that was first discovered in the Unakas Mountains of North Carolina, from which its name was derived.

Tremolite

Family: Silicate Formula: Ca2(Mg5.0-4.5Fe2+0.0-0.5)Si8O22(OH)2 Color: White, gray, lavender to pink, light green, light yellow Habit: Elongated prismatic, or flattened crystals; also as fibrous, granular or columnar aggregates Crystal system: monoclinic Streak: white Luster: vitreous and silky Cleavage: 56 and 124 degrees Fracture: Tenacity: brittle Hardness: 5-6 SG: 2.99-3.03 Diaphaneity: transparent to translucent Formation: Tremolite is an indicator of metamorphic grade since at high temperatures it converts to diopside. Tremolite occurs as a result of contact metamorphism of calcium and magnesium rich siliceous sedimentary rocks and in greenschist facies metamorphic rocks derived from ultramafic or magnesium carbonate bearing rocks.Tremolite forms a series with actinolite and ferro-actinolite. Other: Pure magnesium tremolite is creamy white, but the color grades to dark green with increasing iron content. Nephrite, one of the two minerals of the gemstone jade, is a green variety of tremolite. fibrous form of tremolite is one of the six recognised types of asbestos. This material is toxic, and inhaling the fibers can lead to asbestosis, lung cancer and both pleural and peritoneal mesothelioma. Fibrous tremolite is sometimes found as a contaminant in vermiculite, chrysotile (itself a type of asbestos) and talc.

Talc

It can be crushed into a white powder that is widely known as "talcum powder." Family: Silicate Formula: Mg3Si4O10(OH)2, Small amounts of Al or Ti can substitute for Si; small amounts of Fe, Mn, and Al can substitute for Mg; and, very small amounts of Ca can substitute for Mg. Color: green, white, gray, brown, or colorless Habit: Crystal system: monoclinic Streak: white to pale green Luster: pearly Cleavage: perfect Fracture: Tenacity: Hardness: 1 SG: 2.7-2.8 Diaphaneity: translucent Formation: found in the metamorphic rocks of convergent plate boundaries. It forms from at least two processes. Most large talc deposits in the United States formed when heated waters carrying dissolved magnesium and silica reacted with dolomiticmarbles. A second process of talc formation occurred when heat and chemically active fluids altered rocks such as dunite and serpentinite into talc. Other: "talcum powder." This powder has the ability to absorb moisture, absorb oils, absorb odor, serve as a lubricant, and produce an astringent effect with human skin. These properties have made talcum powder an important ingredient in many baby powders, foot powders, first aid powders, and a variety of cosmetics. A form of talc known as "soapstone" is also widely known. This soft rock is easily carved and has been used to make ornamental and practical objects for thousands of years. It has been used to make sculptures, bowls, countertops, sinks, hearths, pipe bowls, and many other objects. Although talcum powder and soapstone are two of the more visible uses of talc, they account for a very small fraction of talc consumption. Its hidden uses are far more common. Talc's unique properties make it an important ingredient for making ceramics, paint, paper, roofing materials, plastics, rubber, insecticides, and many other products. Talc has perfect cleavage that follows planes between the weakly bonded sheets. These sheets are held together only by van der Waals bonds, which allows them to slip past one another easily. This characteristic is responsible for talc's extreme softness, its greasy, soapy feel, and its value as a high-temperature lubricant. open pit mine where the rock is drilled, blasted, and partially crushed in the mining operation. The highest grade ores are produced by selective mining and sorting operations. Partially crushed rock is taken from the mine to a mill, where it is further reduced in particle size. Impurities are sometimes removed by froth flotation or mechanical processing. The mills usually produce crushed or finely ground talc that meets customer requirements for particle size, brightness, composition, and other properties.

Kaolinite

It is an important industrial mineral. It is a layered silicate mineral, with one tetrahedral sheet of silica (SiO4) linked through oxygen atoms to one octahedral sheet of alumina (AlO6) octahedra.[7] Rocks that are rich in kaolinite are known as kaolin /ˈkeɪ.ə.lɪn/ or china clay.[8] Family: Silicate Formula: Al2(OH)4Si2O5 Color: White to cream, sometimes red, blue or brown tints from impurities and pale-yellow; also often stained various hues, tans and browns being common. Habit: Rarely as crystals, thin plates or stacked, More commonly as microscopic pseudohexagonal plates and clusters of plates, aggregated into compact, claylike masses Crystal system: triclinic Streak: white Luster: pearly to dull earthy Cleavage: Fracture: Tenacity: flexible but inelastic Hardness: 2-2.5 SG: 2.16-2.68 Diaphaneity: opaque Formation: produced by the chemical weathering of aluminium silicate minerals like feldspar. In many parts of the world it is colored pink-orange-red by iron oxide, giving it a distinct rust hue. Lighter concentrations yield white, yellow, or light orange colors. Alternating layers are sometimes found, as at Providence Canyon State Park in Georgia, United States. Commercial grades of kaolin are supplied and transported as dry powder, semi-dry noodle, or liquid slurry. Other: It is described as a 1:1 or TO clay mineral because its crystals consist of stacked TO layers. Each TO layer consists of a tetrahedral (T) sheet composed of silicon and oxygen ions bonded to an octahedral (O) sheet composed of oxygen, aluminum, and hydroxyl ions. The main use of the mineral kaolinite (about 50% of the time) is the production of paper; its use ensures the gloss on some grades of coated paper.[55] Kaolin is also known for its capabilities to induce and accelerate blood clotting. In April 2008 the US Naval Medical Research Institute announced the successful use of a kaolinite-derived aluminosilicate infusion in traditional gauze, known commercially as QuikClot Combat Gauze,[56] which is still the hemostat of choice for all branches of the US military.

Milky Quartz

Milk quartz or milky quartz is the most common variety of crystalline quartz. The white color is caused by minute fluid inclusions of gas, liquid, or both, trapped during crystal formation,[ making it of little value for optical and quality gemstone applications Family: Silicate Formula: SiO2 Color: white Habit: Crystal system: Streak: colorless Luster: Cleavage: Fracture: Tenacity: Hardness: 7 SG: 2.6 Diaphaneity: Formation: Other:

Topaz

One of the worlds favorite colored gemstones, mineral for number 8 on MHS, hardest silicate mineral Family: Silicate Formula: Al2SiO4(F,OH)2 Color: Natural colors include: colorless, yellow, orange, brown, red, pink, blue, green. Occurs in a wide range of treated colors, most often blue. Habit: Crystal system: orthorhombicc Streak: colorless Luster: vitreous Cleavage: perfect basal cleavage Fracture: Tenacity: Hardness: 8 SG: 3.4-3.6 Diaphaneity: translucne to transparent Formation: The fluorine in its composition is a limiting factor on its formation. Fluorine gas in concentrations high enough to form minerals only occurs in a few geologic environments. Most topaz grows as crystals within the veins and voids of igneous rocks. This topaz is found in the cavities of a pegmatite, or in the vesicles and intergranular spaces of rhyolite. These topaz crystals grow during the late stages of magma cooling and while degassing releases the fluorine necessary for topaz crystal growth. Precipitating in cavities, topaz sometimes develops nicely formed crystals. These crystals can have excellent clarity and can be used as a gem material. Many mineral collectors enjoy collecting gem-quality topaz crystals because they have the value of an excellent mineral specimen plus the value of a gem material. Topaz is also found as water-worn pebbles in stream sediments derived from the weathering of pegmatites and rhyolites. These are often produced by placer mining. Other: When allowed to grow in an unrestricted cavity, topaz forms orthorhombic crystals, often with striations that parallel the long axis of the crystal. It also has a distinct basal cleavage that breaks to form vitreous fracture surfaces perpendicular to the long axis of the crystal. This cleavage makes topaz a more fragile gemstone than its hardness of 8 would imply. Topaz is very hard, but it is also brittle and cleaves easily. most natural topaz is colorless. The most highly regarded colors are the reds and pinks, which receive their color from trace amounts of chromium. Chromium is also responsible for the color in violet and purple topaz. A variety known as "imperial topaz" is especially valuable because people enjoy its reddish orange to orangy red colors, which often both occur in the same crystal. Most of the world's imperial topaz is found in Brazil. Topaz with a natural blue color is very rare and valuable. Yellow, brown, and colorless topaz have lower values. These colors are often heated, irradiated, coated, and treated in other ways to alter their color. used for yellowish gemstones for at least two thousand years. At that time yellowish gems were called "topaz" Today most topaz offered in department stores and mall jewelry stores at low to moderate prices has been treated in a laboratory. Colorless topaz can be heated, irradiated, and coated with thin layers of metallic oxides to alter its color. Natural blue topaz is extremely rare and is usually pale blue. Almost all of the blue topaz offered in stores today is colorless topaz that has been irradiated and then heated to produce a blue color. "Swiss blue" and "London blue" are trade names for two of the most common varieties of treated blue topaz seen in today's market. Natural pink to purple topaz is also extremely rare, but these colors can be produced in a laboratory as well. The starting point is a stone cut from colorless topaz. It is first heated and then coated with a layer of metallic oxide to produce the pink color. If coated stones are worn in jewelry, over time the coating can wear thin or wear through at points on the stone where abrasion occurs. Some topaz is coated with a metallic oxide that gives the stone a multicolored iridescent luster. These stones, known as "mystic topaz," appear to change color if the observer moves the stone under a light or changes the angle of observation. These coatings are also thin and can be worn through during normal wear The type of irradiation used to transform colorless topaz into blue topaz can cause the irradiated material to become slightly radioactive. Fortunately, the radioactivity level of the topaz begins to decline as soon as treatment is complete. It eventually declines to a level that is safe for the topaz to be handled during manufacturing and be sold to the public in jewelry..

Smoky Quartz

color-variety of crystalline quartz. It ranges from a light yellowish brown to a brown that is so dark that it appears to be black. Less-desirable specimens have a grayish brown color. When cut as a gem, stones with an orangish brown to a reddish brown color are preferred by many people. Family: Silicate Formula: SiO2 Color: Light yellowish brown to orangish brown to reddish brown to brown so dark that it appears to be black. Many specimens are grayish. Often zoned. Habit: Crystal system: hexagonal Streak: colorless Luster: vitreous Cleavage: none Fracture: conchoidal Tenacity: Hardness: 7 SG: 2.6-2.7 Diaphaneity: transparent to translucent Formation: The color of smoky quartz is produced when natural radiation, emitted from the surrounding rock, activates color centers around aluminum impurities within the crystalline quartz. mainly found in quartz veins and pegmatite dikes that cut across igneous and metamorphic rocks. Well-formed crystals are often found in cavities of igneous and metamorphic rocks along the margins of a pegmatite. Smoky quartz formed at lower temperatures is sometimes found in fractures of sedimentary and metamorphic rocks with no known igneous association. Radioactive mineral deposits in many parts of the world are associated with very dark smoky quartz. The very dark quartz at these locations was probably colored by emissions from the radioactive minerals. Other:

Chalcedony

composed of very fine intergrowths of quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monoclinic. Family: Silicate Formula: SiO2 Color: commonly white to gray, grayish-blue or a shade of brown ranging from pale to nearly black Habit: Crystal system: trigonal or monoclinic Streak: white Luster: waxy, vitreous, dull, greasy, silky Cleavage: none Fracture: uneven, splintery, conchoidal Tenacity: Hardness: 6-7 SG: 2.59-2.61 Diaphaneity: translucent Formation: Other: Chalcedony was used in tool making as early as 32,000 BP in Central Australia. In the Bronze Age chalcedony was in use in the Mediterranean region. Hot wax would not stick to it so it was often used to make seal impressions. Chalcedony is more soluble than quartz under low-temperature conditions, despite the two minerals being chemically identical. This is thought to be because chalcedony is extremely finely grained (cryptocrystalline), and so has a very high surface area to volume ratio. It has also been suggested that the higher solubility is due to the moganite component.

Horneblende

group of dark-colored amphibole minerals found in many types of igneous and metamorphic rocks. These minerals vary in chemical composition but are all double-chain inosilicates with very similar physical properties. a rock-forming mineral that is an important constituent in acidic and intermediate igneous rocks such as granite, diorite, syenite, andesite, and rhyolite. It is also found in metamorphic rocks such as gneiss and schist. Family: Silicate Formula: (Ca,Na)2-3(Mg,Fe,Al)5(Si,Al)8O22(OH,F)2 Color: Usually black, dark green, dark brown Habit: Crystal system: monoclinic Streak: white, colorless Luster: vitreous Cleavage: 2 directions intersecting at 124 and 56 degress Fracture: Tenacity: brittle Hardness: 5-6 SG: 2.9-3.5 Diaphaneity: Formation: Other: dark color (usually black) and two directions of excellent cleavage that intersect at 124 and 56 degrees. The angle between the cleavage planes and hornblende's elongate habit can be used to distinguish it from augite and other pyroxene minerals that have a short blocky habit and cleavage angles intersecting at about 90 degrees. The presence of cleavage can be used to distinguish it from black tourmaline that often occurs in the same rocks. primary use might be as a mineral specimen. However, hornblende is the most abundant mineral in a rock known as amphibolite which has a large number of uses. It is crushed and used for highway construction and as railroad ballast. It is cut for use as dimension stone. The highest quality pieces are cut, polished, and sold under the name "black granite" for use as building facing, floor tiles, countertops, and other architectural uses. Hornblende has been used to estimate the depth of crystallization of plutonic rocks. Those with low aluminum content are associated with shallow depths of crystallization, while those with higher aluminum content are associated with greater depths of crystallization. This information is useful in understanding the crystallization of magma and also useful for mineral exploration.

Olivine

group of rock-forming minerals that are typically found in mafic and ultramafic igneous rocks such as basalt, gabbro, dunite, diabase, and peridotite. They are usually green in color. a very popular green gemstone known as peridot. Family: Silicate Formula: Typically (Mg, Fe)2SiO4. Ca, Mn, and Ni rarely occupy the Mg and Fe positions. Color: Usually olive green, but can be yellow-green to bright green; iron-rich specimens are brownish green to brown Habit: Crystal system: Streak: colorless Luster: vitreous Cleavage:poor. brittle with a conchoidal fracture Fracture: Tenacity: Hardness: 6.5-7 SG: 3.2-4.4 Diaphaneity: transparent to translucent Formation: Most olivine found at Earth's surface is in dark-colored igneous rocks. It usually crystallizes in the presence of plagioclase and pyroxene to form gabbro or basalt. These types of rocks are most common at divergent plate boundaries and at hot spots within the centers of tectonic plates. Olivine has a very high crystallization temperature compared to other minerals. That makes it one of the first minerals to crystallize from a magma. During the slow cooling of a magma, crystals of olivine may form and then settle to the bottom of the magma chamber because of their relatively high density. This concentrated accumulation of olivine can result in the formation of olivine-rich rocks such as dunite in the lower parts of a magma chamber. Crystals of olivine are sometimes formed during the metamorphism of a dolomitic limestone or dolomite. The dolomite contributes magnesium, and silica is obtained from quartz and other impurities in the limestone. When olivine is metamorphosed, it is transformed into serpentine. Olivine is one of the first minerals to be altered by weathering. Because it is so easily altered by weathering, olivine is not a common mineral in sedimentary rocks and is only an abundant constituent of sand or sediment when the deposit is very close to the source. Other: an important mineral in Earth's mantle. Its presence as a mantle mineral has been inferred by a change in the behavior of seismic waves as they cross the Moho - the boundary between Earth's crust and mantle. The presence of olivine in Earth's interior is also confirmed by the presence of olivine in xenoliths, which are thought to be pieces of the upper mantle delivered to Earth's surface in the magmas of deep-source volcanic eruptions. Olivine is also an abundant mineral in the lower portion of many ophiolites. These are slabs of oceanic crust (with part of the upper mantle attached) that have been thrust up onto an island or a continent. identified in a large number of stony and stony-iron meteorites. Most olivine is used in metallurgical processes as a slag conditioner. High-magnesium olivine (forsterite) is added to blast furnaces to remove impurities from steel and to form a slag. Olivine has also been used as a refractory material. It is used to make refractory brick and used as a casting sand. Both of these uses are in decline as alternative materials are less expensive and easier to obtain. The chemical composition of most olivine falls somewhere between pure forsterite (Mg2SiO4) and pure fayalite (Fe2SiO4). In that series, Mg and Fe can substitute freely for one another in the mineral's atomic structure - in any ratio. This type of continuous compositional variation is known as a "solid solution" and is represented in a chemical formula as (Mg,Fe)2SiO4. The name "olivine" is used instead of "forsterite" or "fayalite" because a chemical analysis or other detailed testing is needed to determine which one is dominant - if either is dominant. The name "olivine" serves as a quick, convenient, and inexpensive way to put a name on the material. A list of the more common olivine minerals and their composition is given in the table below. Forsterite used for peridot.

Opal

hydrated amorphous form of silica. classed as a mineraloid. two broad classes of: precious and common. Precious displays play-of-color (iridescence), common does not Family: Silicate Formula: SiO2.nH2OIt is amorphous, without a crystalline structure, and without a definite chemical composition (it contains a variable amount of water, as shown by the "n" in its chemical composition). Therefore opal is a "mineraloid" rather than a "mineral." Color: Commonly having a bodycolor of white, yellow, gray, black, or brown; however, the bodycolor of opal can be any color. Some of the most beautiful common opals are red, orange, pink, green,or blue. The play-of-color of precious opal displays spectral colors of red, orange, yellow, green, blue, and viole Habit: Irregular veins, in masses, in nodules Crystal system: amorphous Streak: white Luster: Rough opal can have a dull, pearly, waxy, or vitreous luster. Most opal polishes to a vitreous luster. Cleavage: none Fracture: conchoidal Tenacity: Hardness: 5-6 SG: 2-2.2 Diaphaneity: translucent, opaque Formation: It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl, and basalt. Other: Some opal also has an internal structure that consists of regularly packed spheres, which enables it to behave like a diffraction grating and separate light into its component colors - similar to what is done by a prism. This phenomenon is known as "play-of-color". Together, these properties enable it to be a gemstone, albeit a fragile one.

Microcline

important igneous rock-forming tectosilicate mineral. It is a potassium-rich alkali feldspar. typically contains minor amounts of sodium. It is common in granite and pegmatites. Microcline forms during slow cooling of orthoclase; it is more stable at lower temperatures than orthoclase. Family: Silicate Formula: KAlSi3O8 Color: pink Habit: Can be anhedral or euhedral. Grains are commonly elongate with a tabular appearance. May contain lamellae which formed from exsolved albite. Crystal system: triclinic Streak: white Luster: vitreous Cleavage: Fracture: Tenacity: brittle Hardness: 6-6.5 SG: 2.5-2.6 Diaphaneity: transaprent to translucnet Formation: Other: generally characterized by cross-hatch twinning that forms as a result of the transformation of monoclinic orthoclase into triclinic microcline. Microcline may be chemically the same as monoclinic orthoclase, but because it belongs to the triclinic crystal system, the prism angle is slightly less than right angles; hence the name "microcline" Microcline is identical to orthoclase in many physical properties, and can be distinguished by x-ray or optical examination. When viewed under a polarizing microscope, microcline exhibits a minute multiple twinning which forms a grating-like structure that is unmistakable. Amazon stone, or amazonite, is a green variety of microcline. The chemical compound name is potassium aluminium silicate, and it is known as E number reference E555. It was the subject in 2018 of a Call for technical and toxicological data from the EFSA. In 2008, it (along with other Aluminum compounds) was the subject of a Scientific Opinion of the Panel on Food Additives, Flavourings, Processing Aids and Food Contact Materials from the EFSA.

Jasper

impure variety of silica, usually red, yellow, brown or green in color; and rarely blue. The common red color is due to iron(III) inclusions Family: Silicate Formula: SiO2 Color: Most commonly red, but may be yellow, brown, green or (rarely) blue Habit: Crystal system: hexagonal Streak: Luster: vitreous Cleavage: indiscernable Fracture: Tenacity: Hardness: 6.5-7 SG: 2.5-2.9 Diaphaneity: opaque Formation: Patterns arise during the consolidation process forming flow and depositional patterns in the original silica-rich sediment or volcanic ash. Hydrothermal circulation is generally thought to be required in the formation of jasper. Other: breaks with a smooth surface and is used for ornamentation or as a gemstone. It can be highly polished and is used for items such as vases, seals, and snuff boxes. main component in the silica-rich parts of banded iron formations (BIFs) which indicate low, but present, amounts of dissolved oxygen in the water such as during the Great Oxidation Event or snowball earths

Labradorite

is a feldspar mineral first identified in Labrador, Canada, which can display an iridescent effect. Labradorite is an intermediate to calcic member of the plagioclase series. It has an anorthite percentage (%An) of between 50 and 70. twinning is common. As with all plagioclase members, the crystal system is triclinic, and three directions of cleavage are present, two of which are nearly at right angles and are more obvious, being of good to perfect quality Family: Silicate Formula: Ca,Na)(Al,Si)4O8, where Ca/(Ca + Na) (% anorthite) is 50-70% Color: Gray, gray-white, brown, greenish, pale green, blue, yellow, colorless Habit: Crystals typically thin and tabular, rhombic in cross section, striated; massive Crystal system: Triclinic Streak: white Luster: vitreous to pearly on cleavages Cleavage: Fracture: uneven to conchoidal Tenacity: Hardness: 6-6.5 SG: 2.68-2.72 Diaphaneity: translucent to transparent Formation: occurs in mafic igneous rocks and is the feldspar variety most common in basalt and gabbro. The uncommon anorthosite bodies are composed almost entirely of labradorite.[4] It also is found in metamorphic amphibolites and as a detrital component of some sediments. Other: Labradorite can display an iridescent optical effect (or schiller) known as labradorescence peculiar reflection of the light from submicroscopical planes orientated in one direction (rarely in two directions); these planes have never such a position that they can be expressed by simple indices, and they are not directly visible under the microscope. Labradorescence is not a display of colors reflected from the surface of a specimen. Instead, light enters the stone, strikes a twinning surface within the stone, and reflects from it. The color seen by the observer is the color of light reflected from that twinning surface. Different twinning surfaces within the stone reflect different colors of light. Light reflecting from different twinning surfaces in various parts of the stone can give the stone a multi-colored appearance.

Biotite

name used for a large group of black mica minerals that are commonly found in igneous and metamorphic rocks. micas vary in chemical composition but are all sheet silicate minerals with very similar physical properties. Family: Silicate Formula: K(Mg,Fe)3(AlSi3O10)(F,OH)2 Color: black, dark green, dark brown Habit: Crystal system: monoclinic Streak: white to gray, flakes often produced Luster: vitreous on cleavage faces Cleavage: basal, perfect Fracture: Tenacity: Hardness: 2.5-3 SG: 2.7-3.4 Diaphaneity: thin sheets are transparent to translucent, books are opaque Formation: Other: It is a black mica with perfect cleavage and a vitreous luster on the cleavage faces. When biotite is separated into thin sheets, the sheets are flexible but will break upon severe bending. When held up to the light, the sheets are transparent to translucent with a brown, gray, or greenish color. Biotite has a small number of commercial uses. Ground mica is used as a filler and extender in paints, as an additive to drilling muds, as an inert filler and mold-release agent in rubber products, and as a non-stick surface coating on asphalt shingles and rolled roofing. It is also used in the potassium-argon and argon-argon methods of dating igneous rocks. Biotite and the brown mica known as phlogopite have been known to cause excitement in inexperienced gold panners. A few tiny flakes of these micas swishing in a gold pan can produce bright bronze-colored reflections in the pan when struck by sunlight. These reflections can fool the inexperienced panner into thinking that he has found gold. removes one of these flakes from the pan and pokes it with a pin, it will break

Orthoclase

one of the most abundant rock-forming minerals of the continental crust. Orthoclase is most widely known as the pink feldspar found in many granites and as the mineral assigned a hardness of "6" in the Mohs hardness scale. Family: Silicate Formula: KAlSi3O8 Color: White, gray, pink, reddish, yellow, green, colorless Habit: Crystal system: Streak: white Luster: vitreous, pearly on cleavage faces Cleavage: perfect in two directions interasecting at 90 degrees Fracture: Tenacity: Hardness: 6 SG: 2.5-2.6 Diaphaneity: translucent to transparent Formation: forms during the crystallization of a magma into intrusive igneous rocks such as granite, granodiorite, diorite, and syenite. Significant amounts of orthoclase are also found in extrusive igneous rocks such as rhyolite, dacite, and andesite. Large crystals of orthoclase are found in igneous rocks known as pegmatite. They are normally no more than a few inches in length. During physical weathering, grains of orthoclase are incorporated into sediments and sedimentary rocks such as sandstone, conglomerate, and siltstone. Chemical weathering alters orthoclase into clay minerals such as kaolinite. significant constituent of the metamorphic rocks known as gneiss and schist. These rocks most often form during regional metamorphism when granitic rocks are subjected to heat and pressure at convergent plate boundaries involving continental crust. The orthoclase in these metamorphic rocks is inherited from their igneous protoliths. Other: raw material used in the production of glass, ceramic tile, porcelain, dinnerware, bathroom fixtures, and other ceramics. It is used as an abrasive in scouring powders and polishing compounds. It is also cut as a gemstone. An adularescent gem material known as moonstone is an intergrowth of orthoclase and albite. Orthoclase is also known in igneous rocks found on the moon and on Mars. Orthoclase is an important constituent of igneous rocks brought back from the moon by astronauts. It has also been detected in the igneous rocks of Mars during analyses done by NASA's rovers. a member of the alkali feldspar series. The alkali feldspars include albite (NaAlSi3O8), anorthoclase ((Na,K)AlSi3O8), sanidine ((K,Na)AlSi3O8), orthoclase (KAlSi3O8), and microcline (KAlSi3O8).

Rose Quartz

pink specimens of the mineral quartz. It is abundant, common, and found in large quantities at numerous locations around the world Family: Silicate Formula: SiO2 Color: pink Habit: Crystal system: Streak: colorless Luster: vitreous Cleavage: none Fracture: conchoidal Tenacity: Hardness: 7 SG: 2.6 Diaphaneity: Formation: massive, anhedral occurrences in hydrothermal veins and pegmatites. pink color of rose quartz is attributed to microscopic inclusions of a pink variety of the mineral dumortierite. These inclusions are usually abundant enough to make the rose quartz translucent instead of transparent. Other: Some specimens of rose quartz contain a dense network of fine inclusions that align with the gem's hexagonal crystal structure. If a cabochon is cut so that its base is perpendicular to the c-axis of the quartz crystal, the cabochon might display asterism in the form of a six-ray star. The best star stones have a vivid pink color and a distinct, symmetrical, and well-centered star

Albite

plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. It represents a plagioclase with less than 10% anorthite content. Family: Silicate Formula: NaAlSi3O8 Color: White to gray, blueish, greenish, reddish; may be chatoyant Habit: White to gray, blueish, greenish, reddish; may be chatoyant Crystal system: Triclinic Streak: White Luster: vitreous, typically pearly on cleavages Cleavage: Fracture: uneven to conchoidal Tenacity: brittle Hardness: 6-6.5 SG: 2.6-2.65 Diaphaneity: transparent to translucent Formation: granitic and pegmatite masses (often as the variety Cleavelandite), in some hydrothermal vein deposits, and forms part of the typical greenschist metamorphic facies for rocks of originally basaltic composition. Other: Albite almost always exhibits crystal twinning often as minute parallel striations on the crystal face. Albite often occurs as fine parallel segregations alternating with pink microcline in perthite as a result of exolution on cooling. There are two variants of albite, which are referred to as 'low albite' and 'high albite'; the latter is also known as 'analbite'. Although both variants are triclinic, they differ in the volume of their unit cell, which is slightly larger for the 'high' form. The 'high' form can be produced from the 'low' form by heating above 750 °C (1,380 °F) High albite can be found in meteor impact craters. Upon further heating to more than 1,050 °C (1,920 °F) the crystal symmetry changes from triclinic to monoclinic; this variant is also known as 'monalbite'. Oftentimes, potassium can replace the sodium characteristic in albite at amounts of up to 10%. When this is exceeded the mineral is then considered to be anorthoclase. Used as a gemstone, albeit semi-precious. Albite is also used by geologists as it is identified as an important rock forming mineral. There is some industrial use for the mineral such as the manufacture of glass and ceramics

Lepidolite

rare lithium-rich mica mineral that is usually pink, red, or purple in color. It is the most common lithium-bearing mineral and serves as a minor ore of lithium metal, with rubidium and cesium sometimes being byproducts. When impregnated with quartz, lepidolite is used as a minor gemstone. Flakes of lepidolite are sometimes responsible for the color of pink and red aventurine. Family: Silicate Formula: K(Li,Al3)(AlSi3)O10(OH,F)2 Color: pink, red or purple as their dominant hue. These are the expected colors of lepidolite. The mineral sometimes has a dark tone, which gives it a grayish appearance. Rare specimens of lepidolite are colorless or yellow. Manganese is the cause of color in pink, red and purple lepidolites. Habit: Crystal system: Streak: white to colorless, often sheds tiny flakes Luster: pearly to vitreous Cleavage: perfect in one direction Fracture: Tenacity: Hardness: 2.5-3.5 SG: 2.8-3 Diaphaneity: transparent to translucent Formation: an only form in geochemical environments where high concentrations of lithium are available for mineral formation. Lepidolite is a rare mineral because these geochemical situations rarely occur. The lithium ion is very small, and it does not readily substitute in other minerals. As a result, it is usually one of the last ions to form minerals during the crystallization of a subsurface magma. As other ions are depleted, the residual fluids of magma crystallization become progressively enriched with lithium. During the final stages of crystallization, there might finally be a high enough concentration of lithium present to form discrete lithium minerals such as spodumene, lepidolite, and petalite. Pegmatites, greisens, and hydrothermal quartz veins are rocks of late-stage magmatic crystallization. They are the rocks where much of the world's lithium minerals are found. In these rocks, lepidolite occurs as disseminated particles, aggregates of fine grains, "books" of flat sheets, and aggregates of curved sheets. Most deposits of lithium-bearing minerals formed by igneous processes are small pod-shaped deposits of a few hundred to a few thousand tons where hand mining and hand separation are required. Other: chemical composition that ranges in a solid solution series from that of polylithionite KLi2Al(Si4O10)(F,OH)2 to that of trilithionite K(Li1.5Al1.5)(AlSi3O10)(F,OH)2. This compositional range of lithium mica is known as the lepidolite series. most important use of lepidolite has been as a minor ore of lithium metal. This use was more important in the first half of the 1900s than it is today. Today most lithium is produced from brine and evaporite deposits in South America, where lithium can be extracted more economically. Small amounts of rubidium sometimes substitute for lithium in the lepidolite crystal lattice. When present, the rubidium can be recovered as a byproduct during the extraction of lithium. Lepidolite and pollucite, another lithium mineral that can contain significant amounts of cesium, often occur together. These minerals can be mined for lithium with cesium as a byproduct. Lepidolite is sometimes used as a source of flake mica. It is also used to make glass and as an ingredient in some enamels. Lepidolite can be used as an ornamental stone and is an important constituent in some gem materials.

Rock Crystal

the most abundant mineral in Earth's crust extremely resistant to weathering highly resistant to physical and chemical weathering used to make time pieces because it vibrates at a precise frequency. Two forms, the normal α-quartz and the high-temperature β-quartz, both of which are chiral. The transformation from α-quartz to β-quartz takes place abruptly at 573 °C. Determining mineral for 7. Family: Silicate Formula: SiO2 Color: colorless Habit: 6-sided prism ending in 6-sided pyramid (typical), drusy, fine-grained to microcrystalline, massive Crystal system: α-quartz: trigonal β-quartz: hexagonal Streak: white Luster: vitreous, waxy to dull when massive Cleavage: indisticnt Fracture: conchoidal Tenacity: brittle Hardness: 7 SG: 2.65 Diaphaneity: transparent to nearly opaque Formation: defining constituent of granite and other felsic igneous rocks. It is very common in sedimentary rocks such as sandstone and shale. It is a common constituent of schist, gneiss, quartzite and other metamorphic rocks.[15] Quartz has the lowest potential for weathering in the Goldich dissolution series and consequently it is very common as a residual mineral in stream sediments and residual soils. Generally a high presence of quartz suggests a "mature" rock, since it indicates the rock has been heavily reworked and quartz was the primary mineral that endured heavy weathering. While the majority of quartz crystallizes from molten magma, quartz also chemically precipitates from hot hydrothermal veins as gangue, sometimes with ore minerals like gold, silver and copper. Large crystals of quartz are found in magmatic pegmatites Other: Geological processes have occasionally deposited sands that are composed of almost 100% quartz grains. These deposits have been identified and produced as sources of high-purity silica sand. These sands are used in the glassmaking industry. Quartz sand is used in the production of container glass, flat plate glass, specialty glass, and fiberglass. an excellent abrasive material. Quartz sands and finely ground silica sand are used for sand blasting, scouring cleansers, grinding media, and grit for sanding and sawing. ery resistant to both chemicals and heat. It is therefore often used as a foundry sand. With a melting temperature higher than most metals, it can be used for the molds and cores of common foundry work. Refractory bricks are often made of quartz sand because of its high heat resistance. Quartz sand is also used as a flux in the smelting of metals. a high resistance to being crushed. In the petroleum industry, sand slurries are forced down oil and gas wells under very high pressures in a process known as hydraulic fracturing. This high pressure fractures the reservoir rocks, and the sandy slurry injects into the fractures. The durable sand grains hold the fractures open after the pressure is released. These open fractures facilitate the flow of natural gas into the well bore. vibrate at a precise frequencies. These frequencies are so precise that quartz crystals can be used to make extremely accurate time-keeping instruments and equipment that can transmit radio and television signals with precise and stable frequencies.

Muscovite

the most common mineral of the mica family. It is an important rock-forming mineral present in igneous, metamorphic, and sedimentary rocks. Like other micas it readily cleaves into thin transparent sheets. Family: Silicate Formula: KAl2(AlSi3O10)(OH)2 Color: thick specimens often appear to be black, brown, or silver in color; however, when split into thin sheets muscovite is colorless, sometimes with a tint of brown, yellow, green, or rose Habit: Crystal system: Streak: white, often sheds tiny flakes Luster: pearly to vitreous Cleavage: perfect Fracture: Tenacity: Hardness: 2.5-3 SG: 2.8-2.9 Diaphaneity: transparent to translucent Formation: found in igneous, metamorphic, and sedimentary rocks. In igneous rocks, it is a primary mineral that is especially common in granitic rocks. In granite pegmatites, muscovite is often found in large crystals with a pseudohexagonal outline. These crystals are called "books" because they can be split into paper-thin sheets. Muscovite rarely occurs in igneous rocks of intermediate, mafic, and ultramafic composition. can form during the regional metamorphism of argillaceous rocks. The heat and pressure of metamorphism transforms clay minerals into tiny grains of mica which enlarge as metamorphism progresses. Muscovite can occur as isolated grains in schist and gneiss, or it can be abundant enough that the rocks are called "mica schist" or "micaceous gneiss." Muscovite is not especially resistant to chemical weathering. It is quickly transformed into clay minerals. Tiny flakes of muscovite sometimes survive long enough to be incorporated into sediments and immature sedimentary rocks. It is evidence that these sediments and rocks have not been subjected to severe weathering Other: early use as window panes. In the 1700s it was mined for this use from pegmatites in the area around Moscow, Russia. These panes were called "muscovy glass" and that term is thought to have inspired the mineral name "muscovite." Sheet muscovite is an excellent insulator, and that makes it suitable for manufacturing specialized parts for electrical equipment. Scrap, flake, and ground muscovite are used as fillers and extenders in a variety of paints, surface treatments, and manufactured products. The pearlescent luster of muscovite makes it an important ingredient that adds "glitter" to paints, ceramic glazes, and cosmetics.

Amazonite

trade name used for a green to bluish green to greenish blue gem material that is made into cabochons, beads, and tumbled stones.. a color variety of microcline, a potassium-rich member of the feldspar mineral group. Family: Silicate Formula: KAlSi3O8 Color: Amazonite occurs in color range of bluish green, to green, and rarely, to greenish blue. These colors can be pale, almost pastel, or vivid with a high saturation. The color of amazonite is often interrupted by streaks and inclusions of white quartz or feldspar. The mineral's color is thought to be caused by trace amounts of lead. Habit: Crystal system: triclinic Streak: white Luster: vitreous. cleavage faces sometimes have a pearly luster Cleavage: perfect in two directions, cleavage planes usually interact at 90 degrees. Fracture: Tenacity: Hardness: 6-6.5 SG: 2.6-2.8 Diaphaneity: translucent to opaque Formation: Well-formed crystals of amazonite are usually found in pegmatites, veins, and other cavities. These are underground places where mineral crystals can grow without obstructions. Amazonite granite is found in a few locations. It is sometimes mined and used as a dimension stone or an ornamental stone. Lapidary-size pieces of amazonite are sometimes found while mining pegmatite. These are used for cutting cabochons, making beads, or producing tumbled stones. Other: green color is thought to be caused by trace amounts of lead. The gem was first named "Amazon stone", after the Amazon River - although there are no known occurrences near that river. used as a gem for over 2000 years. It has been found in archaeological excavations of ancient Egypt and Mesopotamia. rarely used to produce mass-market jewelry. It is rarely used because manufacturers have difficulty finding an adequate supply of gem material and because jewelry customers are not familiar with amazonite. Amazonite is occasionally seen in one-of-a-kind jewelry made by a designer who specializes in using unusual gems.

Amethyst

world's most popular purple gem. It is the purple color variety of quartz that has been used in personal adornment for over 2000 years. Family: Silicate Formula: SiO2 Color: Purple Habit: 6-sided prism ending in 6-sided pyramid (typical), drusy, fine-grained to microcrystalline, massive Crystal system: hexagonal Streak: colorless Luster: vitreous Cleavage: none Fracture: conchoidal Tenacity: Hardness: 7 SG: 2.6-2.7 Diaphaneity: transparent to translucent Formation: The first step in amethyst receiving its purple color begins during crystal growth. That is when trace amounts of iron are incorporated into a growing quartz crystal. After crystallization, gamma rays, emitted by radioactive materials within the host rock, irradiate the iron to produce the purple color. The intensity of amethyst's purple color can vary from one part of the crystal to another. These color variations, known as "color zoning," are caused by varying amounts of iron being incorporated into the crystal during different stages of crystal growth. Amethyst crystals grow slowly and the composition of the fluids delivering the iron and the silica needed for crystal growth can vary. The darkest color of amethyst forms when the largest amount of iron is incorporated into the growing crystal. That is what causes color zoning. Color zoning influences the marketability and value of amethyst. Most people want a gem with a rich and uniform color. As a result, gems of uniform color - no color zoning - are the most desirable and the most valuable. Other: Grape agate is actually botryoidal amethyst. The color of amethyst can often be modified by heating. Much of the yellow to golden quartz sold as "citrine" is actually amethyst that has been modified by heating. This heating can be natural or done intentionally by people. Natural or intentional heating can also change the color of amethyst to a pale green. The proper name for this material is prasiolite; however, many sellers call it "green amethyst."