mineral

Pyrite (Fool's Gold)

Iron Disulfide (FeS2)

Hardness: 6-6.5 (Mohs); Color: Brass-yellow to pale gold; Luster: Metallic; Crystal Structure: Isometric/Cubic; Cleavage: Poor/Indistinct; Specific Gravity: 4.8 - 5.0; Streak: Greenish-black to brownish-black.

Hardness: 6-6
Color: Brass-yellow to pale gold
Luster: Metallic

Identified March 21, 2026More mineral →

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Physical properties

Formation & geological history

Formed in high and low-temperature hydrothermal veins, as an accessory mineral in igneous rocks, by contact metamorphism, and in sedimentary rocks like shale and coal. It can form in any geological age where sulfur and iron are present in anoxic conditions.

Uses & applications

Source of sulfur and sulfuric acid; historically used in wheel-lock firearms to create sparks; used as a decorative stone, in costume jewelry (often sold as 'marcasite'), and as a semiconductor in early crystal radio receivers.

Geological facts

Its name comes from the Greek 'pyr' meaning fire because it creates sparks when struck against steel. Despite its nickname, it can sometimes contain small amounts of actual gold, and it is often found in the same geological veins as real gold.

Field identification & locations

Field identification: Harder than gold (cannot be scratched by a copper penny) and brittle (shatters rather than flattens when hit). Commonly found globally, notably in Spain (Rio Tinto), Italy, and the USA. Collectors look for well-defined cubic or pyritohedral crystal shapes.