Bornite Identification Guide

What Bornite Looks Like

Bornite is a copper-iron sulfide famous as "peacock ore" for the brilliant iridescent blue, purple, and red tarnish that develops on exposed surfaces. A truly fresh break is a coppery brown to bronze color (sometimes called copper-red), but it quickly tarnishes to the rainbow sheen. Luster is metallic, and it is opaque. It usually occurs massive or granular rather than as well-formed crystals; crystals, when present, are pseudo-cubic and rare.

Step-by-Step Field ID Checklist

1. Look for a metallic mass with a purple-blue-red iridescent surface film.
2. Break or scratch a small spot to reveal the bronze-brown fresh color underneath.
3. Note metallic luster and opacity.
4. Check hardness with a knife (bornite is fairly soft).
5. Run the streak test, which is the key separator (see below).

Key Diagnostic Tests

• Mohs hardness: ~3; easily scratched by a steel knife or even a copper coin edge.
• Streak: grayish-black. This is diagnostic and separates it from harder sulfides.
• Cleavage/fracture: poor cleavage; uneven to conchoidal fracture, often brittle.
• Specific gravity: high, ~4.9–5.3; it feels heavy.
• Magnetism: non-magnetic (helps separate from pyrrhotite).
• Color test: fresh bronze color plus rainbow tarnish plus dark streak together confirm bornite.

Common Look-Alikes and How to Tell Them Apart

• Chalcopyrite: brass-yellow on fresh surfaces (not bronze), harder (3.5–4), and often artificially tarnished to imitate peacock ore; its fresh color is a clear yellow, not the copper-brown of bornite.
• Chalcocite: dark gray, lacks the strong rainbow tarnish, and is even softer.
• Covellite: indigo-blue with a platy habit and a flexible feel; deeper blue than bornite's tarnish.
• Pyrite: pale brass-yellow, very hard (6–6.5), and gives a greenish-black streak; will not be scratched by a knife.

Where Bornite Is Found

Bornite is a widespread and important copper ore mineral found in hydrothermal copper veins, porphyry copper deposits, and contact metamorphic zones. Notable occurrences include Butte (Montana), the copper districts of Arizona, Cornwall (England), and Kazakhstan, usually alongside chalcopyrite, chalcocite, and other copper sulfides.