section_path: Classification/Non-silicates/Sulfates
section_name: Sulfates
paragraph_text: Sulfates
  
  The sulfate minerals all contain the sulfate anion,. They tend to be transparent to translucent, soft, and many are fragile. Sulfate minerals commonly form as evaporites, where they precipitate out of evaporating saline waters. Sulfates can also be found in hydrothermal vein systems associated with sulfides, or as oxidation products of sulfides. Sulfates can be subdivided into anhydrous and hydrous minerals. The most common hydrous sulfate by far is gypsum, CaSO ⋅2H O. It forms as an evaporite, and is associated with other evaporites such as calcite and halite; if it incorporates sand grains as it crystallizes, gypsum can form desert roses. Gypsum has very low thermal conductivity and maintains a low temperature when heated as it loses that heat by dehydrating; as such, gypsum is used as an insulator in materials such as plaster and drywall. The anhydrous equivalent of gypsum is anhydrite; it can form directly from seawater in highly arid conditions. The barite group has the general formula XSO, where the X is a large 12-coordinated cation. Examples include barite (BaSO), celestine (SrSO), and anglesite (PbSO); anhydrite is not part of the barite group, as the smaller Ca is only in eight-fold coordination.