Silver (on bornite / "Dolomite") "eyes" pendant from Canada.

The mineral bornite is a copper-iron-sulfide having the chemical formula Cu5FeS4. The mineral has an orthorhombic crystal structure. It has a brown to copper red color on a fresh fracture. Oxidation changes color and gets the mineral blue, purple and red hues. The hardness is 3 and the average density is 5.09. After heating bornite is magnetic and it is not radioactive. Bornite is named after the Austrian mineralogist I. von Born (1742-1791). Bornite is often found in pegmatites. It is among others in Arizona, Butte and Mexico. Bornite is an important copper ore, and often occurs together with the much more common chalcopyrite. It is important for the amount of copper that it contains: about 63 mass per cent is copper.