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Colorless Diamond Octahedron
NATIVE ELEMENTS; NON-METALLIC ELEMENTS · ISOMETRIC

Diamond

C

Hardness
10
Streak
White
Spec. Gravity
3.1–3.53
System
Isometric
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About

Diamond has many unequaled qualities and is very unique among minerals. It is the hardest known substance, it is the greatest conductor of heat, it has the highest melting point of any substance (7362° F or 4090° C), and it has the highest refractive index of any natural mineral. Diamond is number 10 on the Mohs scale, and is approximately 4 times harder than Corundum, which is number 9 on the Moh's scale. It also has the most dense atomical configuration of any mineral, and is transparent over the greatest number of wavelengths. Because of heat conduction, Diamonds are cold to the feel at or below room temperature. When heated, a Diamond will remain hot long after the heat source is removed.

The luster of Diamond is excellent. Diamond exhibits great "fire" and brilliance, which gives it a shiny, freshly polished look. Rough Diamonds exhibit a greasy luster, but proper cutting give them a powerful adamantine luster. Only synthetic substances and a few minor gemstones can reach or excel the refractive index of Diamonds.

The hardness and refractive index may slightly vary among Diamond specimens. Bort and Carbonado exhibit a slightly lower hardness than other Diamonds, and lack cleavage. Lonsdaleite (also known as Hexagonal Diamond), is a type of Diamond found with meteorites and is of extraterrestrial origin. It is scientifically a different mineral than Diamond, and believed to have formed when meteoric Graphite fell to earth. When this happened, great heat and stress transformed the Graphite into Diamond, but it retained Graphite's hexagonal crystal lattice.

For additional information, see the gemstone section on Diamond.

Crystal Forms & Aggregates

Most often octahedral, frequently with many crystal faces. Dodecahedral and hexoctahedral crystals, although less common, also occur. Cubic crystals are rare. Crystals may often contain complex growth layers or triangular features known as "trigons".

Diamond also forms in twinned crystals, and as both clean cleavage fragments and unshaped distorted fragments. Some twinned crystals and cleavage fragments assume a triangular shape, which are known as macles. Crystals often have curved faces, and in some cases they be almost round. Another crystal habit is ball-shaped agglomerates of radiating crystals. Diamond also occurs fibrous, massive and as severely distorted crystals.

Other ID Marks

Complex Tests

Diamond is the most inert and durable material, and is not effected by any chemicals.

Striking Features

Immense hardness, adamantine luster, and specific localities

Environment

Varieties

✓ common  · ✗ uncommon

  • Ballas— Diamond in a spherical aggregate with an internal radiating structure.
  • Bort— Dark colored, imperfectly crystallized Diamond that is translucent to opaque.
    In the Diamond trade, a Bort is also a fragment of a gem quality Diamond.
  • Carbonado— Dark gray to black opaque Diamond that exhibits no cleavage and has a specific gravity of 3.1-3.3.
  • Fancy— Refers to colored Diamonds such as blue, red, pink, purple, and green, as well as deep yellow and deep brown. Fancy Diamonds are extremely rare and sought after.
  • Lonsdaleite— Rare, hexagonal polymorph of Diamond, believed to have formed when meteoric Graphite makes an impact on earth. Prior and during the impact, great heat and stress transformed the Graphite into Diamond, though retaining Graphite's hexagonal crystal lattice. Lonsdaleite is found only in a few crater deposits such as the famous Barringer Crater in Arizona. Lonsdale is also know as "Hexagonal Diamond". As it differs in crystal structure, Lonsdaleite is scientifically categorized as an individual mineral species. It is named in honor Kathleen Lonsdale (1903-1971), a crystallographer at the University of London.

Polymorphs

Uses

The most notable use of Diamonds is in the jewelry market. Due to the brilliance, hardness, and rarity of Diamond, it is the most famous of all gemstones. Colorless Diamonds are most often used in jewelry, although recently yellow and brown gems have picked up in popularity. Colored Diamonds such as blue, red, green, pink, and purple, are known as Fancies, and are extremely rare and command exorbitant prices.

Only about 20 percent of Diamonds are fit for gem use. The other 80 percent mined are used industrially, especially as abrasives and as Diamond saws, which are rotary saws with tiny Diamond studs that can cut almost anything. In fact, the only way to cut and polish a Diamond gem is with a Diamond saw. Diamond is also used in thermal insulators, in optics, and in electronics.

Noteworthy Localities

Diamond is more common then perceived, although its environment is very limited, and most Diamonds found are not of the gem variety. South Africa was once the largest producer of Diamonds, and has several famous localities. Most notable is Kimberly, specifically the Kimberly Mine (also known as "The Big Hole"). The surrounding area also contains many productive Diamond mines. Two other famous mines in South Africa are the Premier Mine (Cullinan Mine), in Pretoria; and the Finsch mine in Northern Cape province. Namibia (the coastal region), Sierra Leone, and the Congo are also important African producers of Diamond.
Russia has several Diamond pipes in Siberia, in and around the town of Mirny (Mir) in Yakutia (now Sakha) Republic. The nearby pipes of Udachnaya and Internationalaya are also of note. In China, Diamond has been mined in the Chagma Mine, Yimeng Mountains, Shangdong Prefecture. The Argyle mine in Western Australia is the largest diamond producer in the world by volume, and is also especially noted for producing pink and brown Diamonds. Diamantina, in Minas Gerais, Brazil has produced a unique form of Diamond in a conglomerate matrix.

In the U.S., the Crater of Diamonds State Park, near Murfreesboro, Pike Co., Arkansas is the only Diamond mine in the world open to the public. On average, about two or three Diamonds are found per day from miners trying their luck. In California, in the Gold producing regions of the Sierra Nevada Mountains, several limited Diamond occurrences have been noted, especially where glaciers left waterworn pebbles in placer deposits (such as in Trinity County). Kelsey Lake, Larimer Co., Colorado, contains the only commercially operating Diamond mine in the U.S., which was started in 1996.
A new Diamond field was also discovered in the 1990's in Lac de Gras in the Northwest Territories, Canada, with the Ekati and Diavik Diamond mines making Canada a new and important Diamond producer.

Common Mineral Associations

Distinguishing Similar Minerals

The only mineral that can possibly be be confused with Diamond is waterworn Quartz pebbles which may resemble waterworn Diamonds, but the hardness and luster of Diamond will easily differentiate the two.

Photos

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Crystal forms

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Octahedral
Hexoctahedral
Cubic
Triangular Macle Twin