Gypsum

The most common sulphate mineral. Found as massive material (including the alabaster variety), clear crystals (the selenite variety) and as parallel fibrous aggregates (the satin spar variety). Typically occurs as colourless to white, transparent crystals, thick tabular to lenticular, sometimes prismatic. May dehydrate to the hemihydrate bassanite at elevated temperatures.

Structural context

Gypsum
Crystal System monoclinicSpace Group C2/c
a5.67—10.47 (6.0493)
b14.912—15.21 (15.1344)
c5.556—6.533 (6.293)
alpha90
beta98.97—151.55 (118.3965)
gamma90
volume457.969—984 (496.7295)

Based on 66 measurements

Chemical context

Stoichiometric formulas

Gypsum
mindat.org
  • March 13, 2023CaSO4·2H2O
IMA
  • March 13, 2023Ca(SO4) · 2H2O
mineralogy.rocks
  • Aug. 30, 2022CaS6+O4·2H2O

Elements recorded on EPMA

63
Ca
63
O
63
S
55
H
7
D

Physical properties

ColorColor entities, recognized using a custom trained NER model
  • colourless
  • colourless
    Color noteOriginal color note from the source
    Colourless to white, often tinged other hues due to impurities; colourless in transmitted light.
    StreakStreak entities, recognized using a custom trained NER model
      Streak noteOriginal streak note from the source
      White.
      Lustre
      Vitreous
      Sub-Vitreous
      Silky
      Pearly
      Dull
      Fracture
      Splintery
      Conchoidal
      Transparency
      Transparent
      Translucent
      Opaque
      Tenacity
      flexible
      Hardness
      2
      Measured density
      2.312—2.322
      Calculated density
      2.308