The mineral pyrite, or iron pyrite, is iron sulfide, FeS₂. It has isometric crystals that usually appear as cubes. The cube faces may be striated (parallel lines on crystal surface or cleavage face) as a result of alternation of the cube and pyritohedron faces. Pyrite also frequently occurs as octahedral crystals and as pyritohedra (a dodecahedron with pentagonal faces). It has a slightly uneven and conchoidal fracture, a hardness of 6–6.5, and a specific gravity of 4.95–5.10. It   Its metallic luster and pale-to-normal, brass-yellow hue have earned it the nickname fool's gold due to many miners mistaking it for the real thing, though small quantities of actual gold are sometimes found in pyrite. In fact, such auriferous pyrite is a valuable ore of gold.

Pyrite is the most common of the sulfide minerals. It is usually found associated with other sulfides or oxides in quartz veins, sedimentary rock and metamorphic rock, as well as in coal beds, and as the replacement mineral in fossils.