Pyrite
Iron sulfide (FeS₂)
The brassy iron sulfide mineral famous as 'fool's gold,' known for sharp metallic cubes and a much higher hardness than real gold.
- Mohs hardness
- 6-6.5
- Color
- Pale brass-yellow, metallic
- Type
- mineral
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Overview
Pyrite is iron disulfide (FeS₂), a brass-yellow metallic mineral best known by its nickname "fool's gold" because its color and shine have fooled prospectors for centuries. It is the most common and widespread sulfide mineral on Earth.
Pyrite frequently grows as strikingly geometric cubes, octahedra, and pyritohedra, sometimes with finely striated faces, making it a favorite among mineral collectors. It can also form radiating "pyrite suns" and replace fossils.
Despite the gold comparison, pyrite is harder, lighter, and brittle—and it is genuinely useful as a source of sulfur and as a historic fire-starter.
Formation & geology
Pyrite forms in an enormous range of environments. It precipitates from hydrothermal fluids in veins and ore deposits, crystallizes in igneous and metamorphic rocks, and forms in sedimentary settings such as black shales and coal where oxygen is scarce and bacteria reduce sulfate.
In anoxic muds, pyrite often replaces organic material, producing pyritized fossils and framboidal (raspberry-like) microspheres.
Well-formed cubic crystals come from famous localities such as Navajún, Spain, while Peru, Italy, and the USA produce other notable specimens.
How to identify it
- Color & luster: Pale brass-yellow with a bright metallic luster; tarnishes brownish.
- Hardness: 6-6.5; it will scratch glass, unlike soft real gold (2.5-3).
- Streak: Greenish-black to brownish-black (gold leaves a yellow streak).
- Habit: Cubes, often with parallel striations on faces; brittle and breaks rather than bending.
Versus real gold: Gold is soft, malleable (dents, doesn't shatter), very heavy (specific gravity ~19), and has a golden streak. Pyrite is brittle, lighter (~5), and harder. Chalcopyrite is more golden/iridescent and softer (3.5-4).
Uses & significance
Historically pyrite was mined as a source of sulfur and sulfuric acid, and it was used in early firearms (the "pyrite" in wheellock guns) and to strike sparks.
Today it has limited industrial value but is popular as a collector and decorative mineral, sold as natural cubes, clusters, and polished pieces. Marcasite jewelry traditionally uses cut pyrite.
Pyrite can be a useful ore indicator, since gold and copper deposits are often associated with it. In metaphysical lore it is linked to protection and abundance—cultural claims, not science.
Frequently asked questions
How can you tell pyrite from real gold?
Pyrite is hard (scratches glass) and brittle, with a greenish-black streak. Gold is soft, malleable, very heavy, and leaves a golden-yellow streak.
Why is pyrite called fool's gold?
Its brassy-yellow color and metallic shine resemble gold, fooling inexperienced prospectors despite being a completely different, far less valuable mineral.
Is pyrite worth any money?
Most pyrite is inexpensive, but fine, sharp natural crystals and rare specimens (like Spanish cubes) have real collector value.
Does pyrite rust or break down?
Yes. Pyrite can oxidize in humid air ('pyrite decay'), producing sulfuric acid and crumbling; store specimens dry and cool.
Pyrite guides
In-depth guides for identifying, valuing, and understanding Pyrite.
Pyrite identified by the community
Real specimens identified with Rock Identifier.
