Diamond

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Chemical composition -- Almost pure carbon, crystallized under extremes of heat and pressure.

Color -- Colorless to yellow, brown, orange, blue, green, pink, black. Most diamonds are slightly yellowish, and in this general color range, those most approaching absolute lack of color are most prized. However, brightly colored diamonds are much rarer and more expensive. The deep blue Hope diamond and blue Eugenie diamond, both in the Smithsonian collection, are among the most famous examples. The rarest and most highly prized color is a deep pink to red. A purplish red diamond weighing .95 carat sold in 1987 for US$880,000 -- US$926,000 per carat!

Optics -- R.I. 2.417. Dispersion 0.044 (high).

Durability -- Hardness 10 on Mohs scale. The hardest natural substance. Diamonds can be cut and polished only with other diamonds, and only because of slight directional differences in hardness and a perfect octahedral cleavage. While diamonds are tough, they can be chipped along sharp girdles or facet edges. Diamonds are also highly heat resistant, but they can be burned if subjected to prolonged high heat. This sometimes happens when platinum prongs are retipped by jewelers unfamiliar with the high melting point of platinum; repolishing usually results in minimal weight loss.

Crystal structure -- Isometric (cubic).

Specific Gravity -- 3.515.

Sources -- The major sources include southern Africa, Australia, and Siberia. In North America, the best known source is at Murfreesboro, Arkansas, although it has not been commercially developed. Significant deposits have been found recently in Canada.

Diamond prices and other information.

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