Lonsdaleite
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Lonsdaleite, also called hexagonal diamond in reference to the crystal structure, is an allotrope of carbon with a hexagonal lattice, as opposed to the cubical lattice of conventional diamond. Wikipedia
Elements: carbon
Category: Mineral
Color: Gray in crystals, pale yellowish to brown in broken fragments
Crystal class: Dihexagonal dipyramidal (6/mmm); H-M symbol: (6/m 2/m 2/m)
Crystal habit: Cubes in fine-grained aggregates
Crystal system: Hexagonal
IMA symbol: Lon