The crystals are typically well terminated. The larger crystals are invariably black. Luster is vitreous. Diaphaneity is transparent to opaque in the larger crystals. Crystal Habits include the tetragonal dipyramid, equant and the tabular habit with dominant pinacoid.
Fracture is conchoidal.
Hardness is 5 - 6. Streak is white. Associated Minerals include almost all minerals.