It occurs in hydrothermal deposits associated with sphalerite, pyrite, chalcopyrite, barite and marcasite. Pyrrhotite is often accompanied by pyrite, marcasite and magnetite. Sulfide minerals such as galena, sphalerite, marcasite and pyrite thus form. Pyrite is used to make marcasite jewelry. It is associated with magnetite, ilmenite, anatase, pyrite, marcasite, lepidocrocite and goethite. Pyrite is more stable and less brittle than marcasite. Minerals found in Door County include fluorite, gypsum, calcite, dolomite, quartz, marcasite, and pyrite. Thailand is one of the large producers of modern marcasite jewellery in silver. These are the reasons why pyrite is used instead of real marcasite in "marcasite" jewellery. Ore minerals were galena, sphalerite, calcite, and marcasite. The black shales also contain high amounts of sulfides (marcasite, pyrite) and carbon. Marcasite jewelry does not actually contain the mineral marcasite. The veins contain pitchblende, autunite and uranophane, with accessory marcasite and barite. This problem appears to be significantly worse if any marcasite is present. This disintegration of marcasite in mineral collections is known as "pyrite decay".