It occurs in hydrothermal deposits associated with sphalerite, pyrite, chalcopyrite, barite and marcasite. Minerals identified include haematite, chalcopyrite, tennantite, galena, tetrahedrite, bornite, pyrite, marcasite, enargite and sphalerite. Examples include galena, pyrite and magnetite. The minerals commonly involved in replacement are calcite, silica, pyrite, and hematite. Below that cap is a supergene zone containing pyrite, chalcopyrite, and sphalerite. Shales may also contain concretions consisting of pyrite, apatite, or various carbonate minerals. Soil may contain iron sulfide as pyrite or calcium sulfate as gypsum. The faults are of limited width, filled with calcite, pyrite and remoulded clay. Some sulfur dioxide is also produced by roasting pyrite and other sulfide ores in air. Pyrite and amorphous iron sulfide along with carbon produce the black coloration. It occurs in a wide range of minerals including arsenopyrite, pyrite and magnetite. Pyrrhotite is often accompanied by pyrite, marcasite and magnetite. Orthoclase, staurolite, pyrite, and fluorite often show penetration twinning. Other mineral deposits are silver, copper, pyrite, and limestone. Gold is frequently found in nature associated with minerals containing arsenic and pyrite.