The heavily striated pseudohexagonal tabular crystals are real classics for the mineral collector and often command an equally classic price. Since chalcocite is a secondary mineral that forms from the alteration of other minerals, it has been known to form pseudomorphs of many different minerals. A pseudomorph is a mineral that has replaced another mineral atom by atom, but it leaves the original mineral's crystal shape intact. Chalcocite has been known to form pseudomorphs of the minerals bornite , covellite , chalcopyrite , pyrite , enargite , millerite , galena and sphalerite . Pseudo means false and morph means shape or form, thus pseudomorph means false shape since the mineral is chalcocite but the shape is that of a covellite crystal, for example.
Color is dark gray to black.
Luster is metallic. Crystals are opaque. Crystal Habits include pseudohexagonal tabular to prismatic crystals often with a shallow pyramidal truncation with a flat point. Also found massive and compact. Twinning is common and sometimes results in a six pointed star shaped cyclic twin called a trilling or in elbow shaped twins.