Pyrite is the mineral with the formula FeS₂ commonly called fool’s gold.
Its brassy yellow metallic appearance can resemble gold, especially in freshly broken crystals. Pyrite is an iron sulfide, and it commonly forms cubic crystals with striated faces. Unlike gold, it is brittle and can be scratched more easily.
The name comes from the Greek word pyr, meaning “fire,” because pyrite can produce sparks when struck against steel. It occurs in many geological settings, including sedimentary rocks, hydrothermal veins, and metamorphic rocks. It is also common in coal deposits.
Pyrite was historically mined as a source of sulfur and sometimes used to produce sulfuric acid. It is not the same mineral as chalcopyrite, another brassy sulfide that contains copper. Pyrite can weather to iron oxides and sulfuric acid, contributing to acid mine drainage.