Gypsum: Processed and used as prefabricated wallboard or as industrial or building plaster, used in cement manufacture, agriculture and other uses. Thailand and Cambodia are the world's major suppliers of zircon with large deposits near the border of the two countries. Vietnam, Burma, Sri Lanka and Africa also provide a large supply of these marvelous gemstones to the world market. GYPSUM, the sulphate of calcium with two molecules of water, CaSO4.2H2O, is one of the most important industrial minerals in India. Three varieties of gypsum are known namely: • Selenite • Alabaster • Satin Spar Selenite is crystalline. It is transparent to tanslucent. Massive variety is known as alabaster and fibrous or silky variety as satinspar, both pure white to dull white in colour unless otherwise tingled due to impurities. Commercial deposits are mostly found as marine beds. Gypsum is classed under minerals of evaporite group, though vein deposits and massive deposits in the limestone country formed due to interaction of limestone with sulphurous water are not uncommon. Bedded deposits are found associated with anhydrite (CaSo4, anhydrous gypsum), limestone, shale and clay. Gypsum beds are devoid of fossils. The origin of gypsum has been a subject of great interest in the past and continues to be a research problem for geologists today.
The mineral name gypsum is so old that it is not known who originated its use. It was derived from the Greek word gypsos which means plaster. Originally it referred to the form of gypsum which has been heated to a high temperature to drive off the water in its crystal structure; this is called calcined gypsum. Gypsum is found in nature in mineral and rock form. As a mineral, it can form very pretty, and sometimes extremely large, crystals. As a rock, gypsum is a sedimentary rock, typically found in thick beds or layers. It forms in lagoons where ocean waters high in calcium and sulfate content can slowly evaporate and be regularly replenished with new sources of water. The result is the accumulation of large beds of sedimentary gypsum. Because it is deposited in this environment, it is common for gypsum to be associated with rock salt and sulfur deposits. Gypsum belongs to a group of minerals called the sulfates, and is the most common of the approximately 150 sulfate minerals. Sulfates are compounds of one or more metals with oxygen and sulfur. The oxygen and sulfur join together to form the sulfate ion, SO4-2. Technically, gypsum is hydrous calcium sulfate because it has water in its crystal structure, CaSO4.2H2O. A secondary and minor source, of raw calcium sulfate is the mineral anhydrite. Anhydrite is chemically very much like gypsum, but lacks the water molecule in its crystal structure. Its chemical formula is CaSO4. Gypsum is very soft at 2 on Mohs' hardness scale. It is so soft that a fingernail can easily scratch it. Gypsum crystals can be a number of attractive colors, ranging from completely colorless to tan and even green. Sedimentary gypsum is nearly always white or gray in color. Sedimentary gypsum is the gypsum that is mined as a commodity. During the Middle Ages, zircon was believed to contain remedial power, protecting the wearer from diseases and banishing insomnia. The name "zircon" is believed to have derived from the Arabic words, "zar", meaning gold, and "gun", meaning color. It was discovered in Germany in 1789 by Martin Klaproth.
The most significant use for gypsum is for wallboard and plaster products. All modern homes in Iran and other developed countries use a great deal of wallboard for interior walls. Some gypsum is used to make Portland cement, and some is used in agricultural applications. A small amount of very pure gypsum is used in glass making and other specialized industrial applications. Gypsum is chiefly utilized in the manufacture of ammonium sulphate fertilizer (NH4)2SO4, plaster of Paris, distemper and cement. A considerable quantity of gypsum is used as manure. It is a good soil conditioner and gives growth of peas, beans and alfalfa. Gypsum and anhydrite can be a good source of sulphur. Anhydrite has been utilized in the UK and West Germany for the extraction of sulphur. The use of gypsum for the manufacture of gypsum-stucco for making tiles, roof planks and board products is fast increasing in USA. Stucco is the industrial name for the product obtained from the calcination of gypsum to hemihydrate stage. Gypsum has the very useful property of becoming plastic like mass when heated upto 175ºC. At this temperature it loses about 3/4th of the water molecules. The product thus obtained is known as plaster of Paris. It can be mixed with water, spread and cast into different forms and sizes. It can be mixed with expanded perlite and vermiculite and made into wall plaster and castings.
Gypsum is a by-product of some industrial processes. Although mined gypsum will remain the primary source of this commodity for decades to come, about one-fourth of current gypsum production is provided as a by-product of some industrial processes. There is presently no substitute for gypsum in the production of Portland cement.