Bornite

Bornite (Cu₅FeS₄)is one of the lesser copper ore minerals, mostly copper and sulfur with a little iron. What makes it stand out is the amazing metallic blue-green color it turns after exposure to the air. That gives bornite the nickname peacock ore. Bornite has a Mohs hardness of 3 and a dark gray streak.

Copper sulfides are a closely related mineral group, and they often occur together. In this bornite specimen are also bits of golden metallic chalcopyrite (CuFeS₂) and areas of dark-gray chalcocite (Cu₂S). The white matrix is calcite. I'm guessing that the green, mealy-looking mineral is sphalerite (ZnS), but don't quote me.

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