Diamond

Town in Newton County, southwest Missouri; population (1990) 800. It is situated 19 km/12 mi southeast of Joplin. George Washington Carver, the noted scientist long associated with Alabama's Tuskegee Institute, was born here. His home, to the southwest of the town, is now part of the George Washington Carver National Monument.


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Experiments

Using a device known as a diamond-anvil cell, a moderate force applied to the small tips of two opposing diamonds can be used to attain extreme pressures of millions of atmospheres or more, allowing scientists to subject small amounts of material to conditions that exist deep within planet interiors.

In 1999 US scientists turned a diamond into a metal using a very powerful laser to compress it.

Cutting

Rough diamonds are often dull or greasy before being polished; around 50% are considered ‘cuttable’ (all or part of the diamond may be set into jewellery). Gem diamonds are valued by weight (carat), cut (highlighting the stone's optical properties), colour, and clarity (on a scale from internally flawless to having a large inclusion clearly visible to the naked eye). They are sawn and polished using a mixture of oil and diamond powder. The two most popular cuts are the brilliant, for thicker stones, and the marquise, for shallower ones. India is the world's chief cutting centre.

Noted rough diamonds include the Cullinan, or Star of Africa (3,106 carats, over 500 g/17.5 oz before cutting, South Africa, 1905); Excelsior (995.2 carats, South Africa, 1893); and Star of Sierra Leone (968.9 carats, Yengema, 1972).

Practical uses

Because diamonds act as perfectly transparent windows and do not absorb infrared radiation, they were used aboard NASA space probes to Venus in 1978. The tungsten carbide tools used in steel mills are cut with industrial diamond tools.

Varieties

There are four chief varieties of diamond: well-crystallized transparent stones, colourless or only slightly tinted, valued as gems; boart, poorly crystallized or inferior diamonds; balas, an industrial variety, extremely hard and tough; and carbonado, or industrial diamond, also called black diamond or carbon, which is opaque, black or grey, and very tough. Industrial diamonds are also produced synthetically from graphite. Some synthetic diamonds conduct heat 50% more efficiently than natural diamonds and are five times greater in strength. This is a great advantage in their use to disperse heat in electronic and telecommunication devices and in the production of laser components.

Sources

Diamonds may be found as alluvial diamonds on or close to the Earth's surface in riverbeds or dried watercourses; on the sea bottom (off southwest Africa); or, more commonly, in diamond-bearing volcanic pipes composed of ‘blue ground’, kimberlite or lamproite, where the original matrix has penetrated the Earth's crust from great depths. They are sorted from the residue of crushed ground by X-ray and other recovery methods

History

Diamonds were known before 3000 BC and until their discovery in Brazil in 1725, India was the principal source of supply. Present sources are Australia, the Democratic Republic of Congo (formerly Zaire), Botswana, Russia (Yakut), South Africa, Namibia, and Angola; the first two produce large volumes of industrial diamonds. Today, about 80% of the world's rough gem diamonds are sold through the De Beers Central Selling Organization in London.