The Diamond

Hardest Naturally Occurring Substance on Earth

The diamond is hardest naturally occurring substance on Earth. This characteristic, together with its brilliance and sparkle, makes the diamond the most popular of all gemstones.

Because of its extreme hardness, the diamond also has important industrial applications. The weight of both gem and industrial diamonds is expressed in metric carats. One carat equals one fifth of a gram.

Diamonds are crystals of pure carbon that have been subjected to tremendous pressure and heat. They were probably formed millions of years ago in molten lava at depths of 100 miles or more. As the lava flowed to the Earth's surface through vents known as pipes, it cooled and solidified into kimberlite, a blue rock known to diamond miners as blue ground. Diamonds also mined from alluvial gravels and glacial tills. In 1962, diamonds were for the first time mined from the ocean floor.

Although diamonds have been found on all continents, India was the only known source before the 6th century and remained the primary source until the 18th century. Today, most of the world's diamonds are mined in African countries. Zaire produces mostly industrial diamonds; South Africa is the major source of gem-quality diamonds. They are also found in Borneo, Brazil, Siberia and Australia. In the U.S., diamonds are found in Arkansas, the Upper Peninsula of Michigan and Colorado.

Gem Diamonds

A very high refractive power, together with reflection, and dispersion, gives the diamond its extraordinary brilliance. Of all gems the diamond has the highest index of refraction: 2.419.

Diamonds come in a spectrum of colors from colorless to black; they may be transparent, translucent or opaque. Gem diamonds are primarily transparent and colorless, or nearly so. But most diamonds are tinged with color, which, if sufficiently intense, is prized as a gem and called a fancy. Blue and pink diamonds are the most valuable. Red diamonds are very rare. Clear white diamonds are called diamonds of the first water. Most industrial diamonds are gray or brown and are translucent or opaque.

When found or mined, diamonds look like fragments of glass. Two or more gems are usually cut from a rough stone. Diamond gems have been cut in many different shapes. The brilliant cut is the most popular. This has 58 facets, 33 above the girdle (circle at greatest diameter) and 25 below. The task of the highly skilled diamond cutter is to place the facets so that the most light rays will reflect through the top facets.

Industrial Diamonds

In even the best gem-producing areas only about 25 % of the diamonds mined are of gem quality. The rest, of poor gem quality because of color or faults, are used in industry.

Diamonds are employed by the lapidary (gem cutter) to shape and polish diamonds and other gems. Tiny holes drilled in diamonds are used to draw ductile metals like copper into extremely fine wire for the electronics industry. The stones are also used to true the surfaces of precision grinding wheels. In machine shops, tools tipped with diamonds perform precision-cutting tasks. Geologists and engineers use diamond-tipped hollow steel bits for drilling deep rock formation samples.

Since 1960, companies in a number of countries have produced synthetic diamonds on a commercial scale. In 1990 a new synthetic process was developed that makes diamonds that are harder, heavier, and better heat conductors than natural diamonds.

Diamond History

The word diamond comes from the Greek term adamas, which means "unconquerable." They were initially used for to engraving other gems like sapphire cameos, and for drilling holes in hard, stone beads. Romans believed that diamonds had the power to ward off evil and wore them as talismans, a habit they inherited from Indian culture.

Diamonds were not used as gems in European jewelry until the late 13th century, but a French law of the time decreed that only the king could wear them. In the symbolism of gemstones, the diamond represents steadfast love and is the birthstone for April.

The largest rough diamond ever found was the Cullinan, 3,106 carats, discovered in 1905 in South Africa. In 1907, the Transvaal government presented it to King Edward VII. It was cut into 9 major stones, including the largest world's gem diamond, the Cullinan 1, or Star of Africa, weighing 550.20 carats. This is mounted in the British Royal Scepter and housed in the Tower of London.

Unique Diamond Properties

  • Hardness: Diamond is a perfect "10", defining the top of the hardness scale. Diamond is 4 times harder than the next hardest natural mineral, corundum (sapphire and ruby).
  • Clarity: Diamond is transparent over a larger range of wavelengths (from the ultraviolet into the far infrared) than is any other substance.
  • Thermal Conductivity: Diamond conducts heat better than anything does - five times better than the second best element, Silver.
  • Melting Point: Diamond has the highest melting point (3820 degrees Kelvin)
  • Lattice Density: The atoms of Diamond are packed closer together than are the atoms of any other substance.


Crystal System
10.0 (Mohs' scale)
Specific Gravity
Perfect in 4 directions
Color, Transparency,
Luster & Streak
Color: Colorless to Various
Transparency: Transparent to sub-translucent
Luster: Adamantine to waxy
Streak: White
Associated minerals are limited to those found in kimberlite rock, an ultramafic igneous rock composed mostly of olivine.

-- Bob Katz

Desert Minerals & Geology Index

Things To Do: Rockhounding



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