It occurs associated with nyerereite, alabandite, halite, sylvite, fluorite and calcite. Evaporite deposits may contain potassium minerals such as sylvite and carnallite. Potassium chloride is extracted from minerals sylvite, carnallite, and potash. Only sylvite outranks carnallite's importance in potash production. The mineral sylvite was also named for Sylvius. An example is a bleb of sylvite within chlorite. Closer to 10 percent sylvite followed by Carnallite form. Potassium occurs in many minerals, such as sylvite (potassium chloride). It occurs naturally as the mineral sylvite, and in combination with sodium chloride as sylvinite. Salt domes contain anhydrite, gypsum, and native sulfur, in addition to halite and sylvite. Sylvite, along with quartz, fluorite and halite, is used for spectroscopic prisms and lenses. Common examples of halides include halite (NaCl, table salt), sylvite (KCl), fluorite (CaF). Sylvite is the official mineral of Saskatchewan. Sylvite is found in many evaporite deposits worldwide. Caesium chloride occurs naturally as impurities in carnallite (up to 0.002%), sylvite and kainite.