chalcocite

Copper pyrites (or yellow ore), erubescite (or purple ore), and chalcocite (or grey ore) are the most important.

Chalcocite occurs in vein deposits as one of the important copper ores, especially at Butte, Montana.

The ore chalcocite, sometimes called copper glance, has a metallic luster, often tarnished green or blue.

Both chalcocite and chalcopyrite frequently occur in silver-bearing rocks.

The mineral is harder than chalcocite, but less hard than pyrite, being easily scratched with a knife.