A sulphide mineral, FeS2; sp. gr. 4.9–5.2; hardness 6.0–6.5; cubic; pale brass-yellow, does not tarnish; greenish-black streak; metallic lustre; crystals cubic, pyritohedra (pentagonal dodecahedra), octahedra, or combinations of the two; cleavage poor basal {001}; occurs with other sulphide ores genetically associated with basic and ultrabasic rocks, and together with pyrrhotite and chalcopyrite; very widely distributed in a great variety of environments, and found in igneous rocks as an accessory mineral, in sedimentary rocks (especially black shales), as nodules in metamorphic rocks, and common in hydrothermal veins, in replacement deposits, and contact metamorphic rocks; alters to iron sulphate and limonite. It was formerly used widely for the production of sulphuric acid. Compare marcasite.