Covellite

Covellite, Copper Sulphide, formula CuS

Crystal system: Hexagonal
Hardness: 1.5 to 2
Density: 4.7
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.