Gypsum: Properties, production and applications

Gypsum is the most common sulfate mineral on earth and is commonly associated with halite, anhydrite, sulfur, calcite and dolomite in recent coastal (sabkha or salina) and/or continental (playa) evaporite deposits. Gypsum can appear as transparent crystals (selenite); fibrous, elongated crystals (stain spar); granular and compact masses (alabaster); and in rosette-shaped aggregates called desert roses. The calcium sulfate-water system occurs as three principal solid phases: gypsum (CaSO₄.2H₂O), bassanite (CaSO₄.0.5H₂O), and anhydrite (CaSO₄). Only gypsum and anhydrite are stable phases of these three phases. Uncalcined gypsum and calcined gypsum are consumed in large quantities worldwide, principally for use in the construction and agricultural industries. In building, it is used in plaster, plaster of Paris, wallboard, cement, and ceramic tiles. In agriculture, it is used as an amendment to neutralize sodic soils and to promote the growth of vegetables. World resources of gypsum are large and widely distributed. The top producing countries of gypsum in 2009, in descending order, are China, Iran, Spain, United States, Thailand, Japan and Canada. In 2009, crude and uncalined gypsum production in United States were estimated to be 9.4 and 7.7 million tons, respectively. The average values per metric ton reported by U.S. producers in 2009 were $8.5 for crude gypsum and $40.0 for calcined gypsum. Demand for gypsum products is expected to decreases in the coming decade as housing starts continue to drop.