Lonsdaleite is a hexagonal polymorph of the carbonallotropediamond, believed to form when meteoricgraphite falls to Earth. The great heat and stress of the impact transforms the graphite into diamond, but retains graphite's hexagonal crystallattice. Lonsdaleite is currently found only in Barringer Crater (also known as Meteor Crater) in Arizona and at Canyon Diablo[?]. It was first discovered in 1967.
Lonsdaleite is also known as "hexagonaldiamond." 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.
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