Luster is adamantine. Crystals are translucent to transparent. There is no perpendicular mirror plane and therefore a hemimorphic crystal can be seen, in some rare examples, with differing terminations at the top and bottom of the crystal. Also found massive. Cleavage is sometimes distinct in three directions forming rhombohedrons.
Fracture is conchoidal.
Streak is red. Associated Minerals include pyrargyrite , silver , tetrahedrite , calcite , quartz , galena , sphalerite and other silver vein minerals. A white film forms on the surface of crystals upon exposure to light. Best Field Indicators are crystal habit, density, association with pyrargyrite and color.