The sulfate chlorides are double salts containing both sulfate (SO42–) and chloride (Cl–) anions. They are distinct from the chlorosulfates, which have a chlorine atom attached to the sulfur as the ClSO3− anion. Many minerals in this family exist. Many are found associated with volcanoes and fumaroles. As minerals they are included in the Nickel-Strunz classification group 7.DG. The book, Hey's Chemical Index of Minerals groups these in subgroup 12.2.