Gypsum

Hydrated Calcium Sulfate
CaSO₄.2H₂O

As the gypsum directly enters into chemical reaction, the higher the percentage of CaSO₄.2H₂O content in gypsum the better is the plant performance and the greater is the production of ammonium sulphate.

The History Says

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 Present Scenario

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.

Hardness	Associated Minerals	Streak	Colour	characteristics	Luster	Field Indicators
2 and can be scratched by a fingernail	halite calcite sulphur pyrite borax	white	usually white, colorless or gray, but can also be shades of red, brown and yellow	thin crystals are flexible but not elastic, meaning they can be bent but will not bend back on their own. Also some samples are fluorescent. Gypsum has a very low thermal conductivity (hence it's use in drywall as an insulating filler). A crystal of Gypsum will feel noticeably warmer than a like crystal of quartz	vitreous to pearly especially on cleavage surfaces	crystal habit, flexible crystals, cleavage and hardness

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.

Specifications

The silica (SiO₂) and sodium chloride (NaCl), should not be more than 6% and 0.01% respectively, and it should be free from clayey meterial. As the gypsum directly enters into chemical reaction, the higher the percentage of CaSO₄.2H₂O content in gypsum the better is the plant performance and the greater is the production of ammonium sulphate. Ammonium sulphate is manufactured by reacting ammonium carbonate and powdered gypsum and the calcium carbonate sludge thus recovered as a by-product is utilized in the manufacture of cement. This is one of the greatest advantages in utilizing gypsum for fertilizer manufacture.

Although gypsum of 75% to 85% purity is used in the manufacture of cement, yet a minimum of 82% CaSO₄.2H₂O is preferred. Nearly 0.04 to 0.05 tonne of gypsum is required per tonne of cement produced. It is mixed with the clinker in the end and then crushed to form cement. It acts as retarder in quick setting of cement.

For the manufacture of Plaster of Paris, selenite crystals of purity varying from 97 to 80% are preferred. Three grades of Plaster of Paris are generally known and manufactured:

• Surgical
• Technical
• Commercial

For surgical grade the selenite should be of the highest purity. Other grades are used for making dolls and castings in pottery industry. Sometimes pure white lumpy gypsum of alabaster type is used for the Plaster of Paris manufacture. For the manufacture of distemper also pure white lumpy gypsum of high purity is required. Gypsum of 75% purity and below is used as manure or as sweet-lime.

World Resources

Gypsum is spread all over the world. It is extensively mined in Europe, the UK, Russia, the USA, Canada and African and Asian countries. In Asia, India is the largest producing country and possesses extensive reserves which are available for export to Ceylon, Japan and other far-east countries. At present Japan is getting supplies of gypsum from Canada.

USA
In the USA, gypsum is mined in many states, the important producing states being California, Iowa, Michigan, Texas and New York. It is found to occur in horizons from Silurian to Pliocene age.

Canada
Canadian deposits are found in British Columbia, Manitoba, New Brunswick, Newfoundland, Nova Scotia and Ontario. The important producing centres are Windemere, British Columbia; Gypsumville and Amarnath, Manitoba; Havelock and Hillsborough, New Brunswick; Flat Bay Station, Newfoundland; Millers Creek, Wentworth, Makay Settlement and Nappan Little Narrows (Cape Breton Island), Cheverie, Milford and Walton in Nova Scotia and Hagersville, Caledonia in Ontario. At Milford, a gypsum bed, of some 135 metres thickness, underlain by dolomite is found. Finely crystalline to selenitic type gypsum is found. Gypsum is worked by quarrying except at Hillsborough, New Brunswick where underground operation is resorted.

Cyprus
Abundant reserves of gypsum are found in Cyprus. It occurs in two well-defined groups of deposits, one in a narrow arcuate zone which is remarkably parallel to the trend of the Kyrenia range, in the north of the island; this includes the important Lupatza gypsum outcrop and the other occurs on the periphery of the Troodos igneous massif. Both these deposits are of upper Miocene age.

Japan
The production comes principally from the northern area of Honshu. There are about 30 mines with an average annual production of 8 lakh tonnes. Domestic production is mainly utilized in the manufacture of cement. Japan imports over a lakh tonnes of uncalcined gypsum per year, mainly from the USA, Mexico and Australia.

West Pakistan
In West Pakistan beds of gypsum along with anhydrite, occur in saline series of salt range. The important deposits located in Jhelum district are at Khewra gorge, Dandot, Chanuwla, Makrach, Dand Khel, Mari Hill and Kalabagh Hill.