Diamond is a mineral, one of two crystalline forms of the element Carbon. It is the hardest substance known, and interior stones are used as abrasives, in certain types of cutting tools, and as phonograph needles.

Gem diamonds were first round in streambeds in India and Borneo; most now come from volcanic pipes in South Africa.

Famous diamonds include the Kohinoor, now among the English crown jewels; the Cullinan, from which 10⁵ stones were cut; and the blue Hope diamond. Synthetic diamonds, produced since 1955, are now widely used in industry, these are created through the utilization of explosive energy to compress carbon.