Bornite is an opaque, reddish-brown sulfide mineral of iron and copper (Cu5FeS4). Bornite is also called "peacock ore" because
of its tarnish when fractured. It 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.
Image source: Mineralogical Information Institute
AND PLANETARY SCIENCE