sulfides
Pyrite
FeS2
- Also known as
- fool's goldiron pyrites
- Crystal system
- cubic
- Hardness
- 6–6.5 on the Mohs scale
- Lustre
- metallic
- Colour
- Brass yellow
- Where it forms
- In an enormous range of settings — hydrothermal veins, sedimentary rocks, coal seams — and it forms strikingly perfect cubes and pentagonal dodecahedra.
- Chiefly from
- Navajun, SpainPeruItalyIllinois, United States
Why it is that colour
Metallic iron sulfide. It is paler and more brassy than gold, considerably harder, and brittle where gold is malleable.
Safety
Safe to handle, but it decays. Pyrite in humid air oxidises to iron sulfates and sulfuric acid — a process collectors call pyrite disease — which destroys the specimen, damages whatever it is stored with, and produces genuinely corrosive residue. Keep it dry. Do not put it in water, which accelerates the reaction and produces acid.
Where it comes from
Extremely common and cheap. Spanish cubes from Navajun are the most recognisable specimens in mineralogy.
Historical use
Struck against flint, pyrite throws sparks, and it was part of the standard fire kit in the European Neolithic — Otzi the Iceman carried pyrite and flint. Industrially it was the main source of sulfur for sulfuric acid before the petroleum industry took over.
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
Its name is from the Greek for fire, because it sparks when struck, and that property made it genuinely important — pyrite and flint were a fire-starting kit long before steel. But there is little symbolic tradition attached. The modern reputation as a stone of wealth and abundance is New Age and follows straightforwardly from it looking like gold.
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
Pyrite oxidation is the origin of acid mine drainage, which is one of the largest and longest-lasting environmental problems in mining. Expose pyrite-bearing rock to air and water — which is what mining does — and it generates sulfuric acid, which then dissolves other metals out of the rock. The resulting orange, acidic, metal-laden water can flow from abandoned workings for centuries. The Rio Tinto in Spain has been running this way since Roman mining and is so acidic that it is studied as an analogue for Martian chemistry.
The same reaction happens on a shelf, slowly. A pyrite specimen kept in a damp room will eventually crumble and leave acid stains on whatever it was sitting on.
Identity checked against IMA-CNMNC master list, June 2025.