Bornite
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.