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Diamond

Diamond is the hardest mineral on Earth, and this, combined with it’s exceptional lustre and brilliant fire, has made it the most highly prized of all gems. Pure, colourless diamond is the most popular, but other varieties- from yellow and brown to green, blue, pink, red, grey an black- are also found, depending on the impurities present. Because of the uniform arrangement of their constituent carbon atoms, diamond crystals are well-formed- usually octahedral with rounded edges and slightly convex faces. Their perfect cleavage facilitates the early stages of fashioning, but other diamonds can only polish them.

Occurrence

Diamond forms at high temperatures and pressures 80km (50 miles) or more underground. When India and later Brazil were the main producers, most diamond came from secondary sources, such as river gravels. However, since the discovery of diamond in kimberlite rock in South Africa (around 1870), its extraction has involved processing vast quantities of rock. Australia is the main producer today; other localities include Ghana, Sierra Leone, Zaïre, Botswana, Namibia, the former USSR, the USA, AND Brazil.

Remark

Diamonds are graded by cut, colour, clarity and carat (weight) - the four ‘C’s.

Crystal structure	Cubic
Composition	Carbon
Hardness	10
SG	3.52
Rl	2.42
DR	None
Lustre	Adamantine