Gypsum is widely used in drywalls in the construction industry.
Rock gypsum is a soft sedimentary rock that formed from the evaporation of water from shallow seas or salt lakes. It is often found alongside and usually beneath rock salt beds. This is because gypsum is less soluble in water than halite, or rock salt, and so precipitates from a saturated solution first. It is a very soft rock with a hardness of 2 on the Mohs Hardness Scale. The name is derived from the Greek "gypsos" meaning "chalk."
Occurrence
According to the Mineral Collector's Handbook, thick beds of gypsum can cover as much as 100,000 square miles. These large beds of gypsum can be found in the United States in California, Utah, Colorado and New Mexico. Viable quantities of the mineral can be found in Iran, Pakistan, Brazil, Spain and Thailand, and there are several gypsum mines in Canada. Giant crystals of gypsum measuring 8 feet in length have been found in caves near Chihuahua, Mexico. In New Mexico, there is a 270-square-mile stretch of white gypsum sand that has been declared a national monument.
Composition
Gypsum is the hydrated form of calcium sulfate, each molecule of the sulfate being attached to two molecules of water. Gypsum is usually white but can have some coloring due to the presence of impurities. It can occur as green, pink, orange, yellow or red crystals. The mineral is also found deposited from natural hot springs and from volcanic vapors.
Sedimentary Rocks
Gypsum, along with halite and Epsom salt, form a distinct division of sedimentary rocks that are formed by the evaporation of salt water. Other divisions are shale, sandstone, limestone, conglomerate and porphory rock. Almost three-quarters of the Earth's land mass is covered by sedimentary rocks, and you can see a clear example of the different layers or strata in such natural monuments as the Grand Canyon.
Uses
Gypsum has a number of uses, one of the most common being the main constituent alongside paper in drywall boards. It is an ingredient in plaster and in Portland cement. Gypsum has been used since the 1700s as a soil conditioner and fertilizer, and was widely used in the wheat belts of the Great Plains. The mineral was once mined in Montmartre in Paris, which gives a clue to another use, that as Plaster of Paris, which is gypsum that has been heated to remove the water content.
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