The iron sulfide mineral pyrite has been called fool's gold because of its pale, brass yellow color and glistening metallic luster. It is the most widespread and abundant sulfide mineral in rocks of all ages. The cubic, dodecahedral, and octahedral crystals and the fine grain masses may be distinguished from gold by their higher Mohs hardness of 6 to 6.5 and their lower specific gravity of 4.9 to 5.02; pyrite has a greenish black streak, conducts electricity, and generates a weak electric current when heated. Its darker colored isometric crystals distinguish pyrite from the chemically identical marcasite, which has orthorhombic crystals. Pyrite forms large bodies in moderate to high temperature hydrothermal deposits and in contact metamorphic ore deposits, is an accessory in many igneous rocks, and is common in sedimentary beds and metamorphosed sediments. It is mined as a source of sulfur and iron as well as of the impurities gold and copper. Pyrite is readily oxidized to create sulfuric acid, both commercially and naturally; in the latter case it helps form the enriched zone of ore deposits, especially of copper; oxidation also creates limonite, which forms the gossan, or iron capping, or sulfide deposits.