Mainly a product of chemical deposition, often forming a huge ore layer or lens body, occurring in limestone, red shale and sandstone, marl and clay rock, often associated with anhydrite, stone salt, etc., anhydrite layer In the near-surface part, due to the decrease of external pressure, it is converted into gypsum by the action of surface water; at the same time, the volume increases by about 30%, causing the destruction of the gypsum layer.

Identification features: low hardness, a set of extremely complete cleavage, and the shape of various features can be identified, dense block gypsum, with its low hardness and acidity can not be distinguished from carbonate.