Gypsum
Gypsum comes from the Greek word gypsos and has three different variations: gypsum, alabaster (fine-grained gypsum that has been used for centuries for sculpture) and selenite. Selenite is the colourless and transparent variety that shows a pearl like lustre and has been described as having a moon like glow. This transparent form of gypsum was used for windows before glass was invented.
Gypsum is one of the most common minerals in sedimentary environments and is found throughout the world. You can also find it in lakes and seawater. It is composed of calcium sulphate (calcium, sulphur, and oxygen) with two molecules of water, CaSO4·2H2O. Gypsum is usually white, colourless or gray, but can also be shades of red, brown and yellow. When calcined, it is partially dehydrated and becomes a white fine powder - commonly known as plaster of Paris- which hardens when moistened and allowed to dry. Gypsum also improves soil by releasing calcium and thus enabling a better circulation of water and air in the soil. As gypsum contains a large amount of water, it has fire protection properties when used in plasterboard.
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