mineral

Bornite (peacock ore), likely copper sulfide specimen

Bornite, Cu₅FeS₄; possibly mixed with chalcopyrite

AI-generated identification · may be incorrect

Metallic luster with bronze-brown to iridescent blue-green tarnish; Mohs hardness 3–3.25, poor cleavage, opaque, and specific gravity about 4.9–5.3. The pictured rough fragment strongly resembles oxidized/tarnished bornite, though color alone cannot exclude chalcopyrite.

Identified August 20, 2026More mineral →

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Physical properties

Formation & geological history

Forms in hydrothermal copper deposits, commonly with chalcopyrite, pyrite, and quartz; most specimens are Paleozoic to younger depending on the deposit. Iridescence develops through surface oxidation and weathering.

Uses & applications

An important copper ore historically, but small specimens are mainly sold as mineral curiosities or “peacock ore.” It is not suitable for jewelry wear because it is soft and tarnishes readily.

Geological facts

Fresh bornite is typically bronze-brown; vivid purple, blue, and green colors are secondary tarnish rather than the original mineral color. Acid exposure and handling can accelerate surface alteration.

Field identification & locations

Look for unusually heavy mass, metallic appearance, soft hardness, and copper-rich iridescence; a streak, hardness, density, and chemical test are needed for confirmation. Common localities include Arizona, Montana, Mexico, Peru, and Cornwall.