Allotropes of Carbon - Lonsdaleite (hexagonal Diamond)

Lonsdaleite (hexagonal Diamond)

Lonsdaleite is a hexagonal allotrope of the carbon allotrope diamond, believed to form from graphite present in meteorites upon their impact to Earth. The great heat and stress of the impact transforms the graphite into diamond, but retains graphite's hexagonal crystal lattice. Hexagonal diamond has also been synthesized in the laboratory, by compressing and heating graphite either in a static press or using explosives. It can also be produced by the thermal decomposition of a polymer, poly(hydridocarbyne), at atmospheric pressure, under inert gas atmosphere (e.g. argon, nitrogen), starting at temperature 110 °C (230 °F).