GYPSUM

GYPSUM

·        Gypsum CaSO4 · 2H2O

·        Refractive Index: 1.52-1.53

·        Specific Gravity: 2.32

·        Mohs Hardness: 2

-  Gypsum is hydrated calcium sulfate formed by the evaporation of brines. Commercial deposits invariably contain some anhydrite (CaSO4), the anhydrous form of calcium sulfate, and may also contain clay minerals, silica, limestone, dolomite, and soluble chloride and sulfate impurities. Gypsum is beneficiated solely by selective mining and screening. Products are typically white to off-white and range from 80 to 95% purity. The

principal commercial use of gypsum is based upon the ability of calcium sulfate to readily take on and give up water of crystallization. The dihydrate (CaSO4 · 2H2O), as mined, is converted to the hemihydrate form (CaSO4 · 1/2H2O) by partial calcination.  When hemihydrate is then mixed with water, it hardens as it returns to the dihydrate form.