Diamond

In mineralogy, diamond is an allotrope of carbon, where the carbon atoms arranged in a variation of the face-centred cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions. Diamond has the highest hardness and thermal conductivity of any bulk material. Those properties determine the major industrial application of diamond in cutting and polishing tools.

Most natural diamonds are formed at high-pressure and high-temperature conditions existing at depths of 140 to 190 kilometres in the Earth mantle. Carbon-containing minerals provide the carbon source, and the growth occurs over periods from 1 billion to 3.3 billion years. Diamonds are brought close to the Earth surface through deep volcanic eruptions by a magma which cools into igneous rocks known as kimberlites and lamproites. Diamonds can also be produced synthetically in a high-pressure and high-temperature process which approximately simulates the conditions in the Earth mantle. An alternative and completely different growth technique is chemical vapour deposition. Several non-diamond material, which include cubic zirconia and silicon carbide and are often called diamond stimulants, resemble diamond in appearance and many properties. Special gemological techniques have been specially developed to distinguish natural and synthetic diamond stimulants.