Gypsum = CaSO4.2H20 - Dihydrous calcium sulphate - this is the resultant molecule in all calcium sulphate based products including plaster, plasterboard and floor screed basedon Hemi Hydrate and Anhydrite
CaS04 = Anhydrous calcium sulphate = anhydrite - can be harvested as a waste product of acid manufacture as flouro anhydrite (this is what Lafarge Gyvlon is made from) or as a a waste product from coal fired power stations - this goes though a process called calcination which converts what starts of s a composite product to a single molecular arrangement.
2CaSO4.H20 = Hemihydrate
Harvested mainly as waste from coal fired power stations but also occasionally mined gypsum. It goes through a process called autoclavin - high pressure with moisture which converts the coposite material to a single molecular structure depending on the temperatures, pressures and source materials forms one of 2 types.
- Beta hemi hydrate which chrystallises to form big gypsum chrystalls - used for making bagged plasters and plasterboard products - a relativley soft form of Gypsum
Alpha Hemihydrate - used for floor screed and calcium sulphate block manufacture - also a major constituent in plaster of paris - forms small tightly packed gypsum chrystals which makes it relatively hard
Something like 20% of the UK screed market, approx 50% of the french screed market, approx 65% of the German and dutch markets are of this type.
