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Diamond Mineral Facts:

Chemical Formula: C - The Mineral is essentially pure Carbon

Colors: Most diamonds are of industrial quality and therefore dark and opaque, or, at most, translucent. However purer stones are also found, these include gem quality stones. These are transparent and colorless or nearly so. Gem quality stones of gray, brown, green, yellow, blue and red tinted stones are also known, and, with the exception of the blue and red diamonds, these other colors are more common than the colorless, or so-called white stones.

Hardness: 10 - The hardest natural substance known.
Though diamond is rated at a hardness of 10, the hardness of diamonds varies somewhat depending on the direction of testing, that is it is harder in some directions than others. Diamond cutters make use of this differential in polishing the gems.

Density: 3.5

Cleavage: Perfect cleavage parallel to the octahedral faces. {111}

Crystallography: Isometric - hextetrahedral class
The diamond is usually found in distinct crystals the forms on the crystals often appear to be tetrahedrally hemihedral, although the etch figures on cubic faces suggest hexoctahedral symmetry. Octahedrons, tetrahedrons, icositetrahedrons
and combinations of these forms are common, and in nearly all cases the interfacial edges are rounded and the crystal faces curved. Sometimes this curving is so pronounced that the individuals are practically spheres. Twins are common.

Luster:. Adamanitine - the index of refraction is very high.

Optics: (Refractive Index):  2.42

Gem quality Diamond (above)

Boart or Specimen quality Diamond.

Composition, Structure and Associated Minerals:
Diamond has a very strong dispersion of light. In consequence of their strong dispersion, the reflection of light from the inner surfaces of transparent stones is very noticeable, causing them to sparkle brilliantly, with a handsome play of colors. It is this latter fact and the great hardness of the mineral that make it the most valuable of the gems.  Electrified by friction and becomes phosphorescent when rubbed with a cloth. Some stones after exposure to sunlight give off a phosphorescent glow in the dark. The mineral is a nonconductor of electricity. Three varieties of the diamond have received distinct names in the trade. These are:
Gem diamonds, which are the transparent stones;
Bort, or Bortz, gray or black translucent or opaque rounded masses, with a rough exterior and the structure of a crystalline aggregate; and
Carbonado, black, opaque or nearly opaque masses with a crystalline structure, but no distinct cleavage.

Identification and Diagnostics
Diamond can be distinguished by its great hardness, its adamantine luster and its octahedral cleavage. Burns at a high temperature to yield C0₂ gas, leaving no ash. Will burn readily in oxygen gas, giving off a brilliant light.  The only minerals with which diamond is liable to be confused are much softer, and, consequently, there is little difficulty in distinguishing between them.

Occurrence, Localities and Origins:
Because of their durability, diamonds are found as placer deposits in clay, sand or gravel deposits or in the rocks formed by the consolidation of these substances. In placers they are associated with gold, platinum, topaz, garnet, tourmaline and with other heavy minerals. Historically, the placer diamond mines of Brazil, India and Borneo were very productive, the famous Golconda district in India for a long period furnishing most of the gems to commerce.

The African mines were opened in 1867. Since this time they have been major producers of gem material for the world. It is estimated that the quantity of uncut diamonds yielded by the mines near Kimberly alone have amounted in value to the enormous sum of $900,000,000. For many years the output of the African mines was over 95 per cent of the world's output of gem material. The diamonds are found in a kiberlite which occurs in the form of volcanic necks, or "pipes," cutting carbonaceous shales. The igneous rock is much weathered to a soft blue earthy mass known as "blue ground." Near the surface where exposed to the weathering action of the atmosphere the rock is yellow. The diamonds are scattered through the weathered material in quantities amounting to between 0.3 and 0.6 carat per cubic yard.

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Diamond in Kimberlite (above)

Rough and Cut Diamond.

Early Day view of the Premier Diamond Mine in South Africa

For More Info about Diamond as a Gemstone, see:
Diamond - The King of the Gemstones

Nevada Outback Gems