Bornite (Peacock Ore) / Acid-treated Chalcopyrite

Hardness: 3 to 3.5 on Mohs scale. Color: Iridescent brassy yellow, peacock blue, purple, magenta, and green tarnish over a metallic dark grey/bronze body. Luster: Metallic. Crystal Structure: Orthorhombic/Tetragonal. Specific Gravity: 4.9–5.3.

Formed primarily in hydrothermal veins and magmatic deposits associated with basic igneous rocks. Much of the commercial 'peacock ore' on the market is chalcopyrite artificially treated with acid to enhance its iridescent tarnish.

Bornite and chalcopyrite are major copper ores processed for copper extraction. Bright iridescent specimens are widely sold in the metaphysical, lapidary, and mineral collection trades as display pieces.

Natural bornite develops a rainbow tarnish upon exposure to air, earning it the nickname 'Peacock Ore'. Commercial specimens are often chalcopyrite dipped in acid (such as vinegar or acid mixtures) to induce vibrant purple, blue, and green oxidation layers.

Look for a metallic lustre with a bright multicolored, iridescent sheen (blue, purple, magenta, green). It can be distinguished from genuine bornite by streak testing (bornite gives a dark grey-black streak, chalcopyrite gives a greenish-black streak). Found in major copper mining regions like Mexico, USA (Arizona, Montana), Chile, South Africa, and Cornwall, UK.