with hydrocarbons at high temperature in oil fields can reduce sulfate () into hydrogen sulfide (H2S) with a concomitant precipitation of calcite. The process is known as thermochemical sulfate reduction (TSR). Igneous rocks Anhydrite has been found in some igneous rocks, for example in the intrusive dioritic pluton of El Teniente, Chile and in trachyandesite pumice erupted by El Chichón volcano, Mexico. Naming history The name anhydrite was given by A. G. Werner in 1804, because of the absence of water of crystallization, as contrasted with the presence of water in gypsum. Some obsolete names for the species are muriacite and karstenite; the former, an earlier name, being given under the impression that the substance was a chloride (muriate). A peculiar variety occurring as contorted concretionary masses is known as tripe-stone, and a scaly granular variety, from Volpino, near Bergamo, in Lombardy, as vulpinite; the latter is cut and polished for ornamental purposes. A semi-transparent light blue-grey variety from Peru is referred to by the trade name angelite. Other uses The Catalyst Science Discovery Centre in Widnes, England, has a relief carving of an anhydrite kiln, made from a piece of anhydrite, for the United Sulphuric Acid Corporation. Extensive structural damage in the German city of Staufen im Breisgau has occurred since a 2007 geothermal drilling project allowed subsurface water to invade a layer of anhydrite below the city, causing extensive but uneven ground swelling as pockets of the anhydrite converted to gypsum. References Further reading Spencer, Leonard James. Anhydrite. 1911 Encyclopædia Britannica Mineralgalleries.com Minerals.net Calcium minerals Sulfate minerals Evaporite Salt domes Baryte group Luminescent minerals Orthorhombic minerals Minerals in space group 63