The chemical formula of gypsum is Ca[SO4]•2H2O. The crystal is a hydrated sulfate mineral belongs to monoclinic system. The shape of the crystal is usually a rhombic clintheriform. Swallow-tail twin crystal is common, mostly fibrous, granular and dense clumps aggregation. Glassy color; fibrous crystal is silky color. Complete cleavage; lamina is flexible; Mohs hardness: 2; specific gravity: 2.3. Gypsum has many forms: pure colorless transparent crystal is called selenite; snowy white, non-transparent fine grained block is called alabaster; fibrous aggregate with silky color is known as fibrous plaster. When heated and released water, the gypsum becomes calcined gypsum. Gypsum is mainly formed through chemical sedimentation. The gypsum layer sedimentated in lagoon basin is usually with huge scale and coexist with hard plaster stone, rock salt and potassium salt, etc. China has the top gypsum mine reserves in the world, and Yingcheng in Hubei province is the most famous. Gypsum is mainly used to make model, sculpture, chalk, paint, cement and agricultural fertilizer, etc.