Crystals are generally opaque but thin crystals or exceptional specimens can be translucent. Crystals can have a hexagonal cross-section although rarely symmetrical. The typical termination, if seen, appears as the two faces of a dome but is actually two of the four faces of a prism. Also found granular, massive and occassionally acicular aggregates. Cleavage is imperfect in two directions at 56 and 124 degrees.
Fracture is uneven.
Hardness is 5 - 6. Streak is brown to gray. Large crystals have an almost striated or grainy appearance. Associated Minerals are quartz , feldspars , augite , magnetite , micas and many medium grade metamorphic minerals.