Color is gray to black. Luster is metallic. Crystals are opaque. Also found massive, granular and in radiating aggregates. Twinning is common and sometimes results in a star shaped cyclic twin called a trilling .
Fracture is uneven.
Streak is black. Associated Minerals are quartz , bornite , galena , sphalerite , tennantite , chalcocite , chalcopyrite , covellite , pyrite and other sulfides . Best Field Indicators are crystal habit, streak, cleavage and associations.