Peacock Ore Identification Guide

What Peacock Ore Looks Like

Peacock ore is a copper-iron sulfide — most often bornite (Cu5FeS4) and sometimes chalcopyrite (CuFeS2) — named for the iridescent blue, purple, magenta, and gold tarnish film that develops on its surface. Fresh bornite is coppery-bronze ("horseflesh" colored) and tarnishes to its famous peacock sheen. It has a metallic luster and is opaque. Much material sold as peacock ore is actually chalcopyrite that has been acid-treated to force the iridescence.

Quick visual cues

• Metallic luster with rainbow blue-purple-gold surface film
• Bronze or brassy underlying color
• Opaque, often massive granular chunks
• Iridescence is a surface film, not internal play-of-color

Step-by-Step Field ID Checklist

1. Confirm metallic luster and opacity — it should look like tarnished metal.
2. Scratch a streak on unglazed porcelain: bornite and chalcopyrite give a greenish-black to grayish-black streak.
3. Test hardness: soft, 3-4 Mohs; a steel knife scratches it easily.
4. Check the fresh color on a broken edge: bornite is bronze/copper-red, chalcopyrite is brass-yellow.
5. Assess weight: dense and heavy, SG ~4.2-5.1.
6. Check the iridescence pattern: natural tarnish is patchy and muted; acid-treated chalcopyrite is garishly bright and uniform over fresh-broken faces.

Key Diagnostic Tests

• Mohs hardness: 3-4 (soft for a metallic mineral).
• Streak: greenish-black (chalcopyrite) to grayish/pale-black (bornite).
• Cleavage/Fracture: poor cleavage; uneven to conchoidal fracture.
• Specific gravity: ~4.2 (chalcopyrite) to ~5.1 (bornite) — distinctly heavy.
• Magnetism: generally non-magnetic (helps separate from pyrrhotite).
• No acid fizz (it is a sulfide, not a carbonate).

Common Look-Alikes and How to Tell Them Apart

• Chalcopyrite (untarnished): brass-yellow, softer than pyrite (3.5-4 vs 6-6.5), greenish-black streak — peacock ore is often just tarnished chalcopyrite.
• Pyrite (fool's gold): much harder (6-6.5), pale brass, greenish-black to brownish-black streak, and cannot be scratched by a knife.
• Covellite: deep indigo-blue with a more even blue iridescence and platy habit.
• Treated/dyed quartz or hematite "rainbow" pieces: show glassy or non-sulfide luster and harder, non-metallic streaks.
• Natural vs acid-treated bornite: natural tarnish is subdued and patchy; lab-treated pieces are vividly uniform and rub/wear off over time.

The key separators are soft hardness (3-4) + greenish-black streak + high density + bronze underlying color.

Where Peacock Ore Is Found

Bornite and chalcopyrite occur in copper ore deposits worldwide, including Mexico, Peru, Chile, the USA (Montana, Arizona), Morocco, and Kazakhstan. They form in hydrothermal veins, porphyry copper systems, and contact-metamorphic skarns as primary copper ore minerals.