Graphite

Definition

Graphite is a mineral composed of carbon arranged in graphene sheets of six-atom hexagonal rings and stacked in layers. It is the stable form of crystalline carbon at the Earth’s surface and shallow pressure and with increasing pressure converts to diamond, which in the Earth is stable at depths in excess of 150 km. Graphite is a widespread accessory mineral in both terrestrial rocks and meteorites. It may result from the inorganic reduction of carbon dioxide and carbonate, notably by hydrogen, or from the dehydrogenation of organic materials at temperatures in excess of 300 °C. Typically, it crystallizes during metamorphism from precursor carbonaceous material or forms from fluid deposition as a precipitate of CO₂−CH₄−H₂O. It coexists with methane-rich gases over a broad range of temperatures. The discovery of ¹³C-depleted graphite in 3.8 Ga-old rocks from West Greenland triggered a controversy over whether they represent carbon from early organic remains or inorganic...