Chalcopyrite
Chalcopyrite is the world's most important copper ore mineral and produces the striking "peacock ore" that beginners often mistake for bornite. The vivid blue, purple, and gold iridescent tarnish is caused by thin-film oxidation on the surface. Montana's Butte mining district — once called the "Richest Hill on Earth" — produced chalcopyrite alongside silver, gold, and zinc from one of the richest polymetallic deposits ever found.
Physical Properties
Chemical Formula
CuFeS₂
Hardness (Mohs)
3.5–4
Color
Brass yellow, iridescent tarnish (peacock ore)
Luster
Metallic
Crystal System
Tetragonal
Streak
Greenish-black
Cleavage
Imperfect
Specific Gravity
4.1–4.3
🔍 Field Identification Tips
Brassy yellow color (similar to pyrite but softer — hardness 3.5–4, pyrite is 6–6.5). Greenish-black streak. Often shows iridescent tarnish. Much softer than pyrite — a knife easily scratches chalcopyrite but not pyrite. Distinguished from gold by streak (gold = yellow) and brittleness (gold is malleable).
Varieties & Forms
📍 Where to Find Chalcopyrite in the US
Uses & Applications
Primary copper ore (world's most important copper source), collectors specimens (especially iridescent "peacock ore").
💰 Collector Value Guide
Peacock ore specimens: $10–$100. Quality crystalline pieces: $30–$300. Museum copper ore specimens: $50–$500.
Find Chalcopyrite With Our Tools
Use the We Lick Rocks app to identify specimens, find dig sites, and connect with local rockhounds.