Some of the crystals are etched, cavernous and crumbly.
Color varies from reddish brown to orange and very deep carmine-red to black.
Luster is vitreous to waxy to dull on external surfaces and resinous on fractured internal surfaces. Diaphaneity is transparent to translucent in the smaller crystals, while the larger one tend to be opaque. Crystal Habits include well formed, elongated, commonly twinned, monoclinic prisms and equant pseudorhombohedra. Rarely in breccia as sharp, twinned tabular crystals. 3 Streak is reddish-brown.