Calcium sulfate, hemihydrate

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Fine-grain, odorless powder commonly called Plaster of Paris. Hemihydrate calcium sulfate naturally occurs as the mineral bassanite, but is commonly made by partially calcining Gypsum. When mixed with water, plaster of Paris will dry to a hard mass. It is used for wall plasters, wallboard, moldings, and statuary.

Synonyms and Related Terms

bassanite; plaster of Paris; dried calcium sulfate; dried gypsum; plaster;


  • Ingestion may be harmful.
  • Anmol Chemicals: SDS

Physical and Chemical Properties

Composition CaSO4-0.5H2O
CAS 7778-18-9
Melting Point 163 C
Density 2.5 - 2.7 g/ml
Molecular Weight mol. wt. = 145.15

Resources and Citations

  • The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983 Comment: entry 1753