Gypsum is an [[evaporite]], CaSO<sub>4</sub>•2(H<sub>2</sub>O). When dewatered at temperatures above 200°C, it becomes [[anhydrite]]. | Gypsum is an [[evaporite]], CaSO<sub>4</sub>•2(H<sub>2</sub>O). When dewatered at temperatures above 200°C, it becomes [[anhydrite]]. |