Bornite is an important copper ore (it is both a copper and iron sulfide mineral). It forms brittle, granular, or compact masses that on fresh fractures are metallic and brassy. Upon exposure to moisture, bornite tarnishes to a purplish iridescence, for which reason it is commonly called peacock ore. Hardness is 3, streak pale grayish black. Bornite occurs with chalcopyrite and chalcocite, both more important as ores, in copper deposits that typically form as zones of contact metamorphism (see metamorphic rock) and as sulfide ore veins.