Gypsum

Gypsum (CaSO₄.2H₂O) is a common sulfate mineral made of calcium sulfate. Gypsum has been used as a building material for a long time, possibly since the neolithic. Today, it is used in drywall, and as an ingredient of plaster of Paris. It can also be used as a fertilizer. It is softer than most minerals, with a value of 2 on the Mohs scale of mineral hardness. This mineral can be, somewhat, scratched with your fingernail. A fingernail, with a value of 2.5 on the Mohs scale of mineral hardness is in fact higher than the mineral shown above. It is an ingredient of Portland cement. Gypsum was used in ancient Egypt and Mesopotamia by sculptors. It is also used in making surgical and orthopedic cast molds.

Gypsum Media

Gypsum crystals are soft enough to bend under pressure of the hand. Sample on display at Musée cantonal de géologie de Lausanne.
Gypsum works, Valencian Museum of Ethnology
Old Alfarb kiln for making plaster as a construction material
Map of gypsum deposits in northern Ohio, black squares indicate the location of deposits, from "Geography of Ohio", 1923
Large gypsum crystals in Lechuguilla Cave's "chandelier ballroom"
Gypsum crystals in the Cave of the Crystals in Mexico (person at lower right for scale)
Gypsum crystals formed as the water evaporated in Lake Lucero, White Sands National Park
Gypsum veins in the silts/marls of the Tea Green and Grey Marls, Blue Anchor, Somerset, United Kingdom
Gypsum veins in Caprock Canyons State Park and Trailway, Texas
Dunes made of small crystals of gypsum, White Sands National Park

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