Covellite, Copper Sulphide,
Crystal system: Hexagonal
Hardness: 1.5 to 2
Density: 4.7 gms/cm3
Colour: Blue to black, usually with brassy and/or red highlights. Metallic lustre.
Streak: Black, shiny.
Covellite is a secondary mineral formed by the alteration of other sulphides containing copper. It is a minor copper ore usually found in association with other sulphides such as bornite (Cu5FeS4), Chalcocite (Cu2S), and chalcopyrite (CuFeS2). As can be seen, copper can, to a limited extent, be replaced by iron. Fine mineral specimens can be found at Butte, Montana, USA.
The specimen shown comes from Butte, Montana.