Gypsums

Gypsums, more commonly referred to as gypsum, are soft sulfate minerals and related materials composed of calcium sulfate dihydrate (CaSO4·2H2O). Natural gypsum occurs as crystals or massive white to gray or colorless deposits, with a Mohs hardness of about 2 and excellent cleavage in one direction. It forms as an evaporite in sedimentary environments and is widely distributed around the world.

Natural gypsum includes several varieties. Selenite refers to transparent crystalline forms, satin spar to fibrous varieties with a silky luster, and alabaster to fine-grained, often translucent deposits used for sculpture and ornament. When gypsum is heated to about 150–180°C, it loses part of its water and becomes calcium sulfate hemihydrate, known as plaster of Paris. When rehydrated with water, it reverts to the dihydrate form and hardens as it sets.

Extraction and processing involve mining or quarrying gypsum ore, followed by crushing, drying, and milling to produce products such as gypsum plaster, plaster of Paris, and gypsum board (drywall). Gypsum is also used as a cement additive to regulate set time and as a soil amendment to improve calcium and sulfur nutrition in agriculture and horticulture. In art and architecture, alabaster and plaster have long-standing decorative applications.

Environmental and safety considerations include energy use for calcination and management of gypsum dust. Construction and demolition waste, particularly drywall, can be recycled to recover gypsum and reduce landfill burden. Gypsums have a long history of commercial importance and remain essential in modern building practices and manufacturing.