Bornite. Image source: Mineralogical Information Institute.
Bornite is an opaque, reddish-brown sulfide mineral of iron and copper (Cu5FeS4). It is also called "peacock ore" because of its tarnish when fractured. Bornite is found as masses and sometimes as crystals (cubic system) in intrusive igneous rocks and metamorphic rocks. It occurs widely, with concentrations in Chile, Peru, and Tasmania. It alters to chalcocite. Hardness 3, relative density 5.0.