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History and Formation

Diamond is the premium gemstone, the most brilliant, the hardest natural substance. Its name comes from the Greek adámas, "unbreakable". The history and description of diamonds are full of superlatives.

Glass replica of the Koh-I-Noor diamondDiamond gems were certainly known in India 3,000 years ago, and perhaps earlier. Ancient Sanskrit texts mention trade in diamond and describe it as a gemstone. (Shown, a replica of the famous Koh-I-Noor diamond as it may have looked originally.) In fact, India was the major, possibly unique, source of diamonds for thousands of years. Classical works from Rome, Greece, and China refer to these diamonds.

Sources of diamonds are actually quite rare. Diamonds were discovered in Borneo in 700 and Brazil in 1725 as the production from India was waning. Both of these were comparatively minor sources.

The modern era of diamond mining begins with their discovery in Kimberly, South Africa, in 1866. The first diamond found is appropriately called the Eureka Diamond, and that seed has grown into the largest diamond operation in the world. The various South African diamond miners merged to form De Beers Consolidated Mines in the late 19th century, and that company had a monopoly on the diamond trade until about 2005.

Diamonds are found in scattered locations across southern Africa, in Botswana, Zimbabwe, and elsewhere. The wealth created by diamonds has unfortunately funded rebellions, coups, and other wars across Africa, usually through smuggling and illegal trade. The subjects of these sales are called blood diamonds, and considerable effort is made in developed countries to track and halt this activity.

Why are diamonds so rare? Diamonds are formed deep in the Earth's continental plates under high pressure and moderate temperature. Diamond-bearing magma is then pushed near the surface through rare deep volcanic pipes, but not ejected. Eventually, the cooled magma is exposed and weathers away. These formations are referred to as the minerals kimberlite and lamprosite.

Mining and Production

Diamonds are mined both for industrial use and for gemstones. Mining and distribution are still highly concentrated among a few companies. Major sources of diamonds in 2014 were as follows (in thousands of carats):

World Diamond Production 2014
gemstones industrial
Australia 235 10,000
Botswana 16,000 7,000
Canada 11,600
Congo, Rep 60
Congo, DR 4,400 18,000
Russia 23,000 15,000
South Africa 6,500 5,000
Zimbabwe 1,000
World 74,100 65,000

Botswana diamond minersExtraction of diamonds is a high-security operation. At the end of the workday, workers may be x-rayed to see if they swallowed any diamonds. The extracted ore is carefully crushed, machine-sorted, and then sorted by hand. Industrial and gem-quality stones are classified separately, and the gems will ultimately be evaluated individually for gem-cutting.

A diamond intended as a gem will be examined carefully before cutting. The goal is to make the best-looking gem for the intended shape and purpose (for example, in a ring). Although a diamond is very hard vs. scratching, it is a crystal and can be cleaved along certain planar angles. Gem-cutters have developed a library of favorite gem geometries based on these cleaving planes and the best interior angles for refracting light.

Properties and Uses

The properties of diamonds are full of superlatives. The composition of a diamond is carbon, fixed in a lattice of atoms by extraordinarily strong bonds. A pure diamond is clear and refracts (bends) light to an unusual degree. This gives diamonds their "fire" or rainbow glitter. A few atoms of boron as an impurity will turn the diamond blue; nitrogen will yield a yellow or brown color.

Diamond is the hardest natural substance. Only a diamond can scratch diamond. Industrial gems are used as the cutting edge of drills, saws, and other tools. Diamond dust is an abrasive.

Diamond has an extremely high thermal conductivity but low electrical conductivity, unless boron or another impurity is present. These properties plus the strong light refraction are used to identify true diamonds from imitations.

Diamonds can be synthesized. In fact, most of the diamonds for industrial use are manufactured rather than mined. The most common process involves creating a sufficiently high pressure and temperature in a laboratory to convert carbon to diamond. Diamond crystals can also be grown in a vacuum. These diamonds are usually visually identifiable as industrial-grade. In recent years, it has become possible to create perfect gem-quality diamonds. These perfect imitations have not yet begun to affect the trade in gems significantly.

The Hope Diamond in the Smithsonian Institution The signature use of diamonds is, of course, in jewelry. A diamond ring is the traditional sign of marriage. A diamond in other jewelry may be a centerpiece, surrounded by lesser gemstones. Famous large diamonds all have a name and history. The Hope Diamond (now 45 carats) resides in the Smithsonian Institution in Washington, D.C. Its parent blue stone came from India, contributed to the French crown jewels, disappeared after the French Revolution, and was apparently recut before surfacing in London. Other stones have equally interesting stories.

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