The New Student's Reference Work/Gypsum

Gyp′sum. Gypsum is a mineral composed of lime sulphate in combination with water. Translucent varieties are known as selenite, and very fine grades of the material, of white color and special luster, are known as alabaster. When heated, the water of the gypsum escapes and the mineral becomes a white powder. If moistened, this powder "sets." This material is known as plaster of pans, the name being due to the fact that gypsum was early used near Paris for the making of plaster or cement. Plaster is also used as a fertilizer on land. Gypsum occurs in various states of the Union, notably Iowa. Kansas, Michigan, New York, Ohio and Texas. It is also worked to some extent in Arizona, California, Colorado, Montana, Oklahoma, Oregon, South Dakota, Utah, Virginia and Wyoming. The workable beds of gypsum are deposited in salt lakes. As the salt water becomes more and more concentrated, the gypsum is precipitated before the salt. Gypsum is therefore often associated with salt-deposits, but since it is often deposited from water which is not saturated with salt, it is sometimes precipitated from lakes which never deposit salt. Gypsum occurs in many sedimentary rocks in the form of single crystals or in groups of crystals. In some parts of the west, as in parts of New Mexico, the gypsum occurs at the surface, and its fine particles are blown about like sand, making dunes.