Description and Properties
Gypsum is hydrated calcium sulphate. It is a soft white stone. A fine-grained version of it is known as alabaster, and the desiccated version is plaster of Paris.
Gypsum is somewhat soluble in water. It occurs as layers of sedimentary rock and as deposits downstream of volcanic vents or other sources of sulfur. It may take the form of tiny transparent crystals or silky, fibrous "spars". The White Sands of New Mexico (right) are a rare desert of gypsum sand made possible by the dry conditions.
Mining and Production
Gypsum is widespread and mined in great bulk from open-pit quarries. Of the 246 million tonnes mined in 2014, China produced 54%, the United States 7%, and Iran 5%.
Synthetic gypsum is created when the equipment in smokestacks of coal-fired power plants removes unwanted sulfur from the emissions. This is identical to natural gypsum except for texture and can generally be used as such.
Gypsum is used primarily in construction. It is the main component of drywall (sheetrock) and most plaster. Gypsum is also one ingredient of Portland cement.
Plaster is also used to make molds in medicine, in crafts, and in art. Plaster of Paris is gypsum that has been heated to remove the water molecules. When mixed with water again, it will thicken and gradually harden into stone, making it useful for modeling and casting.
As a means of delivering sulfur, gypsum is used as a fertilizer in agriculture.
The fine-grained version of gypsum, alabaster, is used by sculptors, although this was much more common in historical times (right). Other substances are available now.