sulfides
Chalcopyrite
CuFeS2
- Also known as
- peacock orecopper pyrites
- Crystal system
- tetragonal
- Hardness
- 3.5–4 on the Mohs scale
- Lustre
- metallic
- Colour
- Brass yellow, often with an iridescent tarnish
- Where it forms
- In hydrothermal deposits, particularly the porphyry copper systems that supply most of the world’s copper.
- Chiefly from
- ChilePeruArizona, United StatesCornwall, England
Why it is that colour
Copper iron sulfide. The iridescence is a thin tarnish layer, and it can be produced or intensified by treating the surface with acid.
Safety
A copper sulfide. Safe to handle; do not powder, do not put in water. The acid-treated material sold as peacock ore carries residues from the treatment and should be washed and then kept away from food.
Where it comes from
The world’s principal copper ore, mined at enormous scale in Chile and Peru. Most "peacock ore" sold in shops is chalcopyrite that has been treated with acid to produce the iridescent film, and this is very rarely disclosed. True peacock ore is bornite, a different mineral.
Historical use
The basis of the copper industry, and therefore of electrification.
Recorded as history and attributed where possible. That a stone was used for something establishes that people used it, not that it worked.
What is attributed to it, and since when
No traditional attribution. Its modern reputation belongs almost entirely to the peacock ore trade name, and most peacock ore is not a natural material.
Described, not endorsed. Dating a claim is not the same as assessing it — but an association that first appears in a book published in 1985 is not an ancient inheritance, whatever the label says. A sincere account of feeling better is compatible with the stone doing nothing — see the placebo effect.
Sold as this, but not
Worth knowing
Peacock ore is worth pulling apart because two separate substitutions are stacked on top of each other.
First, the name properly belongs to bornite, which tarnishes naturally to blue and purple. Second, almost all material sold as peacock ore is not bornite but chalcopyrite, and its colours were produced by dipping it in acid. The iridescence is a manufactured surface film on a substituted mineral sold under a borrowed name.
None of which makes it a bad object. It is cheap, it is bright, and the copper is real. It is simply not what it says.
Identity checked against IMA-CNMNC master list, June 2025.