a = 5.39, b = 9.33 c = 10.29 [Å]; β = 100°; Z = 2
Mineral.color
Brown to black
Mineral.habit
Usually in "blocks" of thin sheets or as aggregations of foliated thin scales. Includes large, well formed pseudohexagonal prisms up to 12 cm across and 15 cm long.
Mineral.twinning
Contact twins with composition surface on {001} and twin axis {310}