Calcium sulfate, dihydrate

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White lumps or powder that is commonly called by its mineral name of Gypsum. Calcium sulfate dihydrate is used in the manufacture of portland cement. Gypsum is also used as a filler and pigment in paints, enamels, glazes and paper.

Synonyms and Related Terms

native calcium sulfate; precipitated calcium sulfate; gypsum; alabaster; selenite; terra alba; satinite; mineral white; satin spar; light spar; Pigment White 25






  • Noncombustible.
  • ThermoFisher: SDS

Physical and Chemical Properties

  • Soluble in water. Slightly soluble in glycerol. Insoluble in most organic solvents.
  • Gypsum fluoresces purple.
Composition CaSO4-2H2O
CAS 13397-24-5
Mohs Hardness 1.5 - 2.0
Melting Point 100-150 C
Density 2.32-2.36 g/ml
Molecular Weight mol. wt. = 172.2
Refractive Index 1.520; 1.530; 1.523


Characteristics of Common White Pigments

Resources and Citations

  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983 Comment: entry 1753