Diamond

Diamond is composed of carbon and is the hardest known natural substance although it can be shattered with a sharp blow. It also has the highest thermal conductivity of any known material at room temperature. Diamonds form 150-200 km below the Earth's surface at high temperatures (1,050°C-1,200°C) and pressures (45-55 kilobars). They are carried to the surface within kimberlite and lamproites which intrude through the earth's crust. These intrusions form narrow cylindrical bodies called pipes and only a very small proportion have significant diamond content. When pipes are eroded liberated diamonds can accumulate in alluvial deposits and may be found far from their source as their hardness allows them to survive multiple episodes of erosion and deposition. The quality of diamonds is subdivided into gem, near gem and industrial categories. In rare cases up to 90% of diamonds in a deposit are of gem quality, but most economic deposits contain 20% to 40% gem quality diamonds. Current uses for diamond include jewellery, mining and exploration, stone cutting and polishing, computer chip manufacture, machinery manufacture, construction and transportation services. A large proportion of industrial diamond is manufactured and it is possible to produce synthetic diamonds of gem quality