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Natural Occurrence and Processing
The earliest sources of gem diamonds were India and Borneo, where they were found in river alluvium. All famous diamonds of antiquity were Indian diamonds, including the Great Mogul, the Orlov, the Koh-i-noor, and the Regent or Pitt. Other famous diamonds are the Hope (blue), Dresden (green), and Tiffany (yellow). In the early 18th cent., deposits similar to those in India were found in Brazil, mainly of carbonados, though they may have been known as early as 1670. In 1867, a stone found in South Africa was recognized as a diamond. Within a few years, this began a wild search for diamonds, both in river diggings and inland. In 1870–71, dry diggings, including most of the celebrated mines, were discovered. Well-known South African diamond mines are the Dutoitspan, Bultfontein, De Beers, Kimberley, Jagersfontein, and Premier. Russia, Botswana, Congo (Kinshasa), Australia, and South Africa are now the world's major diamond-producing nations; other important countries include Canada, Angola, Namibia, Ghana, and Brazil. The use of diamonds to finance African rebel groups and fuel civil strife led, in 2001 and 2002, to international agreements (the Kimberley Process) designed to certify legitimately mined diamonds, but in 2011 the permitted sale of diamonds from Zimbabwe, where the army has been accused of brutality and human rights violations in diamond mines and diamond revenues support an autocratic government, led to criticism of the certification process.
Synthetic diamonds were successfully produced in the early 1950s; a number of small crystals were manufactured when pure graphite mixed with a catalyst was subjected to pressure of about 1 million lb per sq in. and temperature of the order of 5,000℉ (3,000℃). Synthetic diamonds are now also commercially produced at a lower pressure in a process that heats methane and hydrogen gas into a plasma in a vacuum chamber; the diamond is built up in layers from a substrate through the deposition of vaporized carbon from the methane. Microscopic diamonds also have been produced through other means, including the detonation of explosives containing carbon. Synthetic diamonds are now extensively used in industry, and are also used as gemstones in jewelry.
The Diamond Cartel
The discoveries of 1870–71 in South Africa led to a great number of prospectors staking out claims and securing the diamonds by open-pit or quarry mining. The damage caused by floods and mudslides, unavoidable when there were so many different claims, was an important factor in the series of amalgamations carried on by Cecil Rhodes and Barnett Barnato. Rhodes brought about the merging of their interests in the De Beers Consolidated Mines, Ltd., which established (1889) an effective monopoly over the diamond industry. Loss of diamonds by theft was reduced through the passage of the so-called I.D.B. (Illicit Diamond Buying) Act, which limited the trade to licensed buyers and imposed penalties for the possession of uncut stones without a license. Thefts were further curtailed by the institution of compounds in which the workers live while employed by the company and which they leave only after being thoroughly searched.
Most of the major diamond producers belong to, or have cooperated with, the De Beers–led marketing cartel, formed to maintain the price of diamonds at a high level. De Beers, under Harry Oppenheimer's leadership (1957–84), maintained its dominant position in the industry by using its numerous worldwide companies to buy up new sources of diamonds and to control distribution of industrial diamonds and production of synthetic ones. In the last decades of the 20th cent., however, De Beers' hold over the unpolished diamond market decreased, and in 2000 the company announced it would end to its policy of controlling diamond prices through hoarding and shift its focus to increasing sales.
See V. Argenzio, Diamonds Eternal (1974); A. N. Wilson, Diamonds: From Birth to Eternity (1982); R. Newman, Diamonds: Fascinating Facts (1990); S. Kanfer, The Last Empire (1993).