bornite

Bornite is a copper iron sulfide mineral with the chemical formula Cu5FeS4. It is a copper ore that occurs in hydrothermal veins and porphyry copper deposits and is well known for its iridescent tarnish, which can display a range of purple, blue, pink, and green colors on exposed surfaces. Because of this colorful patina, it is commonly sold as a decorative stone under the name peacock ore. Fresh surfaces are typically bronze to copper-red and have a metallic luster.

Bornite crystallizes in the tetragonal system and commonly occurs as massive, granular, or tabular aggregates. It has a Mohs hardness of about 3 to 3.5 and a specific gravity around 4.3–4.9. It is often found with chalcopyrite, pyrite, sphalerite, and quartz, and its oxidation products include secondary copper minerals such as malachite and azurite.

Ore processing may target bornite in deposits where chalcopyrite is less abundant or where oxidation has altered primary sulfides. It is named after Ignaz von Born, an 18th-century Austrian mineralogist.