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. 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.
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. Last updated 18 May 1998.