an iron sulfoarsenide mineral (FeAsS), the most common ore of arsenic. It is most commonly found in ore veins that were formed at high temperatures, as at Mapimí, Mex.; Butte, Mont.; and Tunaberg, Swed. Arsenopyrite forms monoclinic or triclinic crystals with an orthorhombic shape; the physical appearance of these crystals is seldom an accurate method for determining their symmetry. A series of minerals in which cobalt partially replaces iron is called cobaltian arsenopyrites; those in which the Co:Fe ratio lies between 1:2 and 6:1 are called glaucodot (see also cobaltite). Weathering alters these sulfides to arsenates: arsenopyrite to scorodite, and glaucodot to erythrite. For detailed physical properties, see sulfide mineral (table).