Formation of Diamond

The formation of natural diamond requires very specific conditions. Diamond formation requires exposure of carbon-bearing materials to high pressure, ranging approximately between 45 and 60 kilobars but at a comparatively low temperature range between approximately 1652–2372 °F (900–1300 °C). These conditions are known to be met in two places on Earth; in the lithospheric mantle below relatively stable continental plates , and at the site of a meteorite strike.
Diamonds can also form in other natural high-pressure events. Very small diamonds, known as microdiamonds or nanodiamonds, have been found in meteorite impact craters. Such impact events create shock zones of high pressure and temperature suitable for diamond formation. Impact-type microdiamonds can be used as one indicator of ancient impact craters.