Assignment 7: Diamonds & Diamond Grading

How do crystals affect the behavior of light when they form in less symmetrical crystal systems?

Crystals that form in less symmetrical crystal systems split light rays into separate beams that take different paths and travel at different speeds. These crystals are called doubly refractive, or anisotropic.

What are atoms comprised of structurally?

even smaller subatomic particles: protons, neutrons, and electrons Protons and neutrons form the nucleus, which is the heart of the atom Electrons surround the nucleus in orbits, or shells.

Gem-quality cube-shaped rough diamonds are...

extremely rare

When the atoms in diamond crystal are closer together in some directions this makes those directions...

harder and, as a result, unsuitable for sawing and polishing.

Why termal test a diamond?

it measures thermal conductivity and helps separate diamond from most simulants.

In terms of gem quality, what is the most important factor in a diamond's potential value as a gemstone?

its SHAPE Two crystals with the same color and clarity might be equal in weight, yet one can be worth many times more than the other on the basis of shape alone. This is because the shape affects the amount of weight the cutter can retain in the finished gem. If a crystal is an octahedron or a cube, it's easy to imagine—and cut—at least one large fashioned gem from it. If it's irregular, or even flat, this limits the cutter's choices.

The actual number of electrons in an atom's outer shell determines...

its chemical nature—its ability to combine with other atoms.

How do crystals form?

organically and inorganically—they can grow in plants and animals as well as in molten rock or in the laboratory. In fact, scientists have discovered that almost all solids are crystalline.

The names of crystal shapes come from the number of...

sides or faces on the crystal

What's an atom?

the basic structural unit of all matter

What level of thermal conductivity does diamond have?

the highest If you touch a diamond, it will feel cool because its temperature rises very slowly in response to your body heat.

No matter how they look on the outside, all diamonds have...

the same well-defined internal patterns

Diamonds are hard and tough because of...

the tightness of the atomic bonding.

Mineral crystal internal structures are very uniform because...

they're built from huge numbers of identical unit cells.

How small are atoms?

too small to be seen by the unaided eye One cubic centimeter of solid matter—about the size of a sugar cube—contains billions of atoms.

What are some examples of crystals from daily life?

your teeth and bones; sugar and salt; snow and ice; sand, aspirin, steel, and nylon. And, of course, diamonds.

How can you use SG (specific gravity) to tell diamond from imitators?

Almost all of the common simulants have higher SGs than diamond. Many jewelry professionals can detect a simulant simply because it weighs more than it looks like it should.

What is a crystal axis?

An imaginary line that passes through a crystal. When the crystal is rotated around it, it defines the crystal's symmetry.

What minerals have hexagonal crystal systems?

Apatite and beryl The hexagonal crystal system has four crystal axes. The three lateral ones are equal in length and in the same plane, and they intersect at 60 degree angles. The fourth is often longer and at a right angle to the other three. Beryl such as this rich green emerald is a member of the hexagonal crystal system. Emeralds often form as elongated six-sided crystals with flat faces at each end.

How does thermal expansion and thermal conductivity work on a gem's chemical composition and crystal structure?

As temperature increases, atoms pick up energy. The energy makes them vibrate, and they move farther apart.

How are crystal planes important to a diamond cutter?

Because some crystal planes are best for sawing and polishing and others for cleaving.

What is a bort?

Bort is a form of diamond that usually occurs as very included single crystals in a range of yellows, grays, and browns. While it was once considered suitable only for industrial use, modern designers have adopted bort's more interesting colors and shapes and incorporated them into contemporary jewelry styles.

What is the regular, repeating arrangement of atoms in a mineral called?

CRYSTAL STRUCTURE (a.k.a. CRYSTAL LATTICE)

CRYSTAL SYSTEMS

Categories of crystals based on their symmetry and internal structure There are 7 crystal systems

What is a GLIDE PLANE?

Crystal distortion caused during growth when one part of the lattice is offset in relation to the rest. It happens when the atoms don't stack perfectly during growth and the crystal structure becomes deformed.

The trace element, boron, does what to diamonds?

It colors diamonds blue and makes them electrical conductors.

When an atom has a full outer shell of electrons...

It is chemically inert, which means it won't easily combine with other atoms.

What's thermal conductivity?

It measures the rate at which a gem's surface temperature responds to a change in the temperature of its environment. The higher the thermal conductivity, the slower the change.

What minerals have monoclinic crystal systems?

Kunzite, jade, moonstone The monoclinic crystal system has three unequal axes. Two of them meet at an oblique angle. The third is perpendicular to the other two. The mineral spodumene forms in the monoclinic crystal system. Its best known variety is the pink kunzite. Kunzite often forms as a tall columnar crystal with vertical striations and irregular terminations.

What's a mineral species?

Minerals related by chemical composition and crystal structure make up a species. There are over 3,000 known mineral species, including diamond.

What minerals have triclinic crystal systems?

Most feldspars The triclinic crystal system is the least symmetrical of the seven crystal systems. Triclinic crystals have three unequal axes, all intersecting at oblique angles. The microcline species, part of the feldspar group, forms in the triclinic system. The variety amazonite, often used for ornamental objects, appears blocky with wedge-shaped faces.

Crystal

Natural historians began using the term crystal to describe symmetrical mineral specimens early in the seventeenth century.

What trace element affects the way a diamond absorbs light and produces the color yellow in diamonds?

Nitrogen

What are diamond cleavage planes?

Plane parallel to a possible crystal face, where a diamond can split cleanly when struck.

A mineral's OPTIC CHARACTER is...

The way a mineral handles light

Where does the word, crystal, come from?

The word itself comes from the Greek krystallos , which means "clear ice." Interesting: The Greeks used it to identify rock crystal quartz, a mineral that they found high in the mountains. In its rough form, it probably looked like permanently frozen water to them.

The diamond mineral species includes several varieties based on...

Their property differences: fancy-colored, colorless, and so on.

What's a mineral group?

These are minerals related by structure and properties. In the gemstone world, garnets and feldspars are the most-familiar mineral groups.

Diamond surfaces parallel to the octahedral plans (cleavage planes) have what characteristics?

They are the hardest, very resistant to scratching and impossible to polish.

What makes cubic planes so useful to diamond cutters?

They provide the most efficient directions for sawing large, regularly shaped crystals into sections. The sections can then be cut into standard round brilliants without losing too much weight from the original rough.

Cutters try to polish along a diamond's dodecahedral (12 sides) planes because...

They're the diamond crystal's softest directions

What minerals have orthorhombic crystal systems

Topaz, chrysoberyl, peridot, tanzanite Crystals in the orthorhombic system have three crystal axes at right angles to each other and all of different lengths. Topaz, like this beautiful reddish orange imperial variety, forms in the orthorhombic crystal system. The crystals are typically elongated with chisel-like ends and vertical striations.

When carbon atoms in diamond bond under very high pressure, they...

create a strong, interlocking atomic structure.

What are the 7 crystal systems?

cubic (aka isometric) - the most symmetrical The rest are less symmetrical but have their own physical and optical characteristics. tetragonal hexagonal trigonal rhombohedral orthorhombic monoclinic triclinic

Diamond's CRYSTAL SYSTEM is also called the

cubic or aka isometric system Crystals in the cubic system are the most symmetrical Other minerals that are cubic minerals: Garnet, spinel, platinum, and gold

No matter what shape a diamond has on the outside, on the inside it consists of cube-shaped _____________________ linked together?

diamond unit cells that act like building blocks

What do atoms do as part of matter?

dictate whether matter is living or nonliving, and whether it's animal, vegetable, or mineral - all based on the way they're arranged and combined.

Diamond is singly refractive and thus will never show...

doubling

What are covalent bonds?

- are the strongest atomic bonds. - these are chemical bond formed by two atoms sharing electrons. Each carbon atom shares an electron with each of its four neighbors. That way, it fills its outer shell with eight electrons without losing any of its own electrons. Each neighboring atom does the same thing -- creating covalent bonds

number of protons in the nucleus determine...

....what the element is. It is known as the atomic number.

Because a diamond's unit cell is cube-shaped, it can be the basis of...

...a number of different shapes.

Unit cells connect to build...

...crystal shapes or crystal forms.

The core of diamond's unit cell is formed from...

...four tetrahedrons, held together by shared electrons in strong covalent bonds. Each corner atom in a tetrahedron is connected to an atom of another unit cell. The outer atoms of the tetrahedrons are bonded to atoms of other tetrahedrons, and so on.

Because a diamond's unit cell is cube-shaped, the finished shape depends not so much on the shape of the blocks but on...

...how the blocks are stacked. Cube-shaped blocks can build a pyramid or a larger cube, for example.

A diamond's gem habit is most often expressed as the shape....

...octahedron, a form with eight triangular faces.

Perfectly shaped octahedral diamond rough is...

...so rare it often ends up as a collector's specimen rather than a cut gem.

Crystal shapes can indicate...

...the atomic structure inside a crystal.

Crystals are classified by mineralogists and gemologists based on...

...their geometric properties and the symmetry of their internal crystal structures.

Glassies are...

...well-shaped, transparent, octahedral diamond crystals with sharp, square edges.

What makes diamond a unique member of the gem world?

1) it's made of a single element: carbon. 2) the magnificent simplicity of its internal crystal structure.

The Greek word, Dodeca

12

The Greek word, Tris

3

Diamond's SG (specific gravity) is

3.52, which means a diamond weighs 3.52 times as much as an equal volume of water. NOTE: The SG of industrial diamonds can be as low as 3.43 because of their many inclusions and impurities.

The Greek word, Tetra

4

Diamonds carbon atoms are connected in groups of...

5 - with one in the center and the other four surrounding it. Each outside atom is part of another group of five as well. Each group is called a tetrahedron.

The Greek word, Hexa

6

How many protons does carbon have?

6 protons

The Greek word, Octa

8

What is a SINGLY REFRACTIVE crystal?

A crystal that possesses the same physical or optical properties in all crystal directions.

What is an ISOTROPIC crystal?

A crystal that possesses the same physical or optical properties in all crystal directions.

What is a mineral's HABIT?

A habit is a characteristic crystal shape of a specific mineral.

What's a mineral?

A mineral is a solid material that forms in nature, not as the result of human technology. It's inorganic, which means it's not alive and never was. Each mineral has its own characteristic chemical composition. Most also have a characteristic crystal structure.

How many internal crystal planes does a diamond have?

Diamond has three internal crystal planes: cubic, octahedral, and dodecahedral. All diamonds, regardless of their external appearance, contain all three.

What gives diamond its superior hardness?

Diamond's atoms are closer together than the atoms of any other natural material. This is what gives diamond its superior hardness.

How does crystal structure affect the behavior of light?

In diamond and other cubic crystals, light rays behave the same way no matter which direction they're traveling. These crystals are described as singly refractive, or isotropic

A tetrahedron is

In geometry, a tetrahedron is a four-sided figure with triangular sides. When the word is used to describe diamond structure, it refers to the group of carbon atoms.

What are CLEAVAGE DIRECTIONS?

In some directions there are fewer carbon atoms—with more space between them—than in others. These are called cleavage directions. They're like the spaces between the pages of a book—they make the pages easier to separate than to tear across.

Diamonds that incorporate small crystals of other minerals —even of other diamonds—during the formation process have...

Inclusions you usually need magnification to see these inclusions, but you can sometimes see them with your unaided eye.

What are crystal planes?

Internal directions parallel to a mineral's unit cell surfaces.

What does ANISOTROPIC mean?

Possessing different physical or optical properties in different crystal directions.

What does doubly refractive mean?

Possessing different physical or optical properties in different crystal directions.

Which subatomic particles are electrically charged?

Protons have positive charges and electrons have negative charges.

What minerals have trigonal crystal systems?

Quartz and corundum Gems in the trigonal crystal system have four crystal axes in a similar arrangement to the hexagonal system, but with less symmetry. Quartz is a trigonal gem that usually takes the form of a six-sided crystal topped by a six-sided pyramid. Ruby vs sapphire? Like sapphire, ruby is a variety of the mineral species corundum and a member of the trigonal crystal system. However, the two gems shapes can be very different. Ruby crystals are often flattened, six-sided, and terminated by flat faces.

What is SPECIFIC GRAVITY (SG)

Ratio of the weight of a material to that of an equal volume of water. A cubic meter of a substance with an SG of 1.00 would weigh exactly the same as a cubic meter of water.

What are unit cells?

Smallest group of atoms with the characteristic chemical composition and the basic crystal structure of a mineral. The unit cell's structure sets the standard for repeating patterns throughout the crystal.

Atoms in a gem that aren't part of its essential chemical composition.

TRACE ELEMENTS Trace elements are sometimes called impurity elements.

What is DOUBLING?

The appearance of double images of a gemstone's facet junctions on the side opposite the viewer.

A diamond weighs about 1.6 times as much as the same size piece of graphite because...

The carbon atoms in a diamond crystal are closer together than those in graphite, so there are more of them in the same space.

What are some examples of minerals?

The earth's rocks are made of minerals So are all metals and most building materials. Ceramics used in everything from coffee mugs to spacecraft heat shields are derived from minerals. Glass, many medicines, and even common table salt are made of minerals.

The names for geometric and crystal forms by using the Greek words for numbers and shapes.

Tris = 3 Tetra = 4 Hexa = 6 Octa = 8 Dodeca = 12 Individual roots can be combined to make roots for larger numbers. Tetrahexa = (4× 6) = 24 Trisocta = (3× 8) = 24 Hexocta = (6× 8) = 48 Next, add the base word hedron, which means "face." So, an octahedron has 8 faces, a dodecahedron 12, and a trisoctahedron 24.

What dododecahedral crystals look like?

Usually rounded and without perfectly flat faces. Great for fashioning round brilliants (just like octahedrons)

What is GRAINING in a diamond?

Visible, shadow-like lines in a diamond caused by irregularities in the crystal structure. Graining occurs when conditions change during crystal growth. Several types of graining can appear in diamonds, depending on the nature of the structural irregularities.

How do you distinguish a singly refractive diamond from doubly refractive simulants like zircon, colorless sapphire and other synthetics?

When you look into diamond simulants from most directions, you'll see double images of the facet junctions on the opposite side. The visibility of the doubling

What is mineral has a tretragonal crystal system?

Zircon Gems in the tetragonal crystal system have three crystal axes. Two are of equal length and at right angles to each other and the third is a different length and positioned at a right angle to the planes of the first two. Zircon forms in the tetragonal crystal system, usually as a four-sided prism (a columnar crystal with parallel faces) with pyramid-shaped faces at the end, called terminations.

What's thermal expansion?

a material's capacity to expand when it's heated

What is the periodic table?

a table of the chemical elements arranged in order of atomic number

What is a crystal?

any bit of solid matter with atoms arranged in a regular, repeating pattern

An atom with fewer electrons will....

attract electrons from other nearby atoms in an attempt to always have a full outer shell. An atom is "happy" when there are 8 electrons in its outer shell

Why are internal octahedral planes so important to diamond cutting?

because they are cleavage planes - that is: planes parallel to a possible crystal face, where a diamond can split cleanly when struck.

Each mineral species has varieties that differ in features such as...

color and transparency