Some of the sulfates that may be present in bedrocks are kieserite, sulfate anhydrate, bassanite, hexahydrite, epsomite, and gypsum.
2.
When gypsum is heated in air it loses water and converts first to calcium sulfate hemihydrate, ( bassanite, often simply called " plaster " ) and, if heated further, to anhydrous calcium sulfate ( anhydrite ).
3.
Heat generated in the grinding process causes gypsum ( CaSO 4.2H 2 O ) to lose water, forming bassanite ( CaSO 4.0 . 2-0.7H 2 O ) or ?-anhydrite ( CaSO 4 . ~ 0.05H 2 O ).
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