Types of Gypsum

（CaSO₄･2H₂O / Monoclinic crystal system）
Gypsum, alabaster, selenite, satin spar, phosphogypsum, flue-gas desulfurization gypsum

（CaSO₄･1/2H₂O / Trigonal crystal system）
Bassanite, hemihydrate gypsum

＊Classified into two types by each manufacturing methods:

①α-hemihydrate gypsum / α gypsum, α plaster, dental stone

②β-hemihydrate gypsum / β gypsum, β plaster, plaster of pairs, impression plaster, model plaster,
  casting plaster

（CaSO₄ / shown as below）　
Bassanite, hemihydrate gypsum

＊Classified into three types of crystal systems:

①α-anhydrite (Unknown)

②β-anhydrite (Orthorhombic crystal system) / Natural anhydrite is formed.

③γ-anhydrite (Hexagonal crystal system)