mineral

Bornite (“peacock ore”), likely polished specimen

Bornite, Cu5FeS4

AI-generated identification · may be incorrect

Identified August 29, 2026More mineral →

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Physical properties

Metallic luster; typically bronze-brown to iridescent blue, purple, and gold tarnish; Mohs hardness 3–3.25; opaque, orthorhombic at low temperature, with indistinct cleavage and specific gravity about 4.9–5.3. The blue-gray body and brassy-gold metallic patches are consistent with bornite, though chalcopyrite may be present.

Formation & geological history

A copper-iron sulfide formed mainly in hydrothermal copper-ore deposits and porphyry systems, commonly during the Mesozoic to Cenozoic or older mineralizing events. Its vivid colors are a superficial oxidation/tarnish film developed after exposure or polishing.

Uses & applications

An important historical copper ore and a popular mineral-display specimen; not generally used as a gemstone because it is soft and tarnishes readily. Attractive cabinet pieces may have significant collector appeal.

Geological facts

“Peacock ore” is a trade name for iridescent bornite or chalcopyrite, not a separate mineral species. Fresh bornite is usually darker bronze-brown; intense blue coloration commonly reflects deliberate acid treatment or natural tarnishing.

Field identification & locations

Identify by metallic heft, softness, copper sulfide colors, and blue-purple-gold tarnish; a streak is gray-black, and acid treatment can produce unusually vivid colors. Common localities include Cornwall, England; Butte, Montana; Peru; Mexico; and Kazakhstan.