Lonsdaleite

A hexagonal polymorph of the carbon allotrope diamond, believed to form when meteor?ic graphite falls to earth. The great heat and stress of the impact transforms the graphite into diamond, but retains graphite's hexagonal crystal lattice. Lonsdaleite is currently found only in the famous [Barringer Crater]? (also known as meteor crater) in Arizona and at [Canyon Diablo]?. It was first discovered in 1967.

Lonsdaleite is also known as "Hexagonal Diamond." It has an [index of refraction]? from 2.40 to 2.41, a density from 3.2 to 3.3, and a hardness of 3.00.