Gypsum is a soft sulfate mineral known chemically as calcium sulfate dihydrate, which includes two molecules of water in its crystalline structure. This common mineral is found across the globe and is a fundamental raw material for several major industries. Its primary importance lies in construction, where it is the main constituent of plaster and drywall, providing fire resistance to building materials. The mineral is also broadly used in agriculture as a soil amendment to improve drainage and supply both calcium and sulfur to crops.
Geological Context of Gypsum Formation
The vast majority of commercially viable gypsum deposits are sedimentary in origin, formed through the process of evaporation. This process occurs in restricted marine basins, such as shallow seas or lagoons, where the rate of water loss due to evaporation significantly exceeds the replenishment from freshwater sources. As the seawater concentrates, dissolved minerals precipitate sequentially based on their solubility, forming layered deposits known as evaporites.
Gypsum is one of the first minerals to crystallize from the brine after calcite, typically when about 80% of the original water volume has evaporated. These ancient, massive beds of gypsum and its dehydrated form, anhydrite, are often interbedded with other evaporite minerals like halite, or common rock salt. The conditions necessary for this large-scale deposition—high temperatures and arid climates—were prevalent in many geological periods, resulting in thick, extensive layers preserved within the Earth’s crust. This geological history dictates the current location of the world’s largest gypsum reserves.
Primary Global Evaporite Deposits
The most significant gypsum reserves are concentrated in regions characterized by these ancient, massive evaporite sequences. North America holds major deposits, with extensive reserves found across the United States in states like Iowa, Texas, and Nevada, often mined from large, shallow beds. Canada also contributes substantial volumes, particularly from the maritime province of Nova Scotia, which serves the North American and European markets.
In the Middle East and Asia, countries along the Persian Gulf possess immense reserves. Iran, in particular, has vast deposits distributed across various provinces, making it a major global source. Significant quantities are also found in China, especially in regions like Xinjiang and Inner Mongolia, supporting its massive domestic construction industry. Thailand is another major Asian producer, with its reserves primarily used for cement manufacturing and export.
Europe’s most notable deposits are found in Spain, France, and Germany, where the mineral has been historically extracted for centuries. Spain is a prominent producer, with large deposits resulting from the evaporation of ancient inland seas. Additionally, Mexico’s reserves in areas such as Baja California and Sonora represent a major source that feeds the North American market, confirming the worldwide distribution of these massive, ancient formations.
Secondary and Trace Occurrences
Gypsum is also found in smaller, localized occurrences that do not always support large-scale commercial mining operations. One well-known secondary formation is the “gypsum desert rose,” a unique rosette-shaped cluster of crystals that forms in arid, sandy environments. These formations, which incorporate sand grains into their structure, are commonly found in the Sahara Desert, the Mojave Desert, and parts of the southwestern United States and Mexico.
The mineral can also be found in non-evaporitic geological settings. Gypsum occurs in hydrothermal veins, where sulfate-rich fluids move through rock fractures and precipitate the mineral. It also forms when groundwater hydrates anhydrite layers near the Earth’s surface. Some of the world’s largest gypsum crystals, known as selenite, have been discovered in deep cave environments, such as the famous Naica Mine in Mexico.