Crude gypsum is used as a fluxing agent fertilizer filler in paper and textiles and retarder in Portland cement About threefourths of the total production is calcined for use as plaster of Paris and as building materials in plaster Keenes cement board products and tiles and blocks Parameters Gypsum 1 Gypsum Moisture Content : Max 30 Sieve : Tests 50 mm : NIL 400 mm : MAX 100 5mm : Max 300 SiO : Max 50 MgO : Max 20 SO : Min 380 Total Alkalies as Na O : Max 010 Chloride content : Max 05 Combined Water : Min 163 Purity : Min 780 Parameters Composition Percentage Calcium Oxide CaO 30 Min Sulphuric Anhydrids SO3 42 Min Silicon of Oxide SiO insoluble Matter 2 Max Magnesium Oxide MgO 04 Max Ferric Oxide Fe2O3 04 Max Aluminium Oxide AI2O3 03 Max Moisture 1 Max Gypsum asCaso42H2O 90 Min