Gypsum
Species
Common · CaSO₄·2H₂O
Hydrated calcium sulfate deposited when shallow seas evaporate. The transparent selenite variety can grow into crystals many metres long, as in a cave complex of the Naica mine in Mexico. Dehydrates to plaster of Paris at 150°C.
Identity
- Formula
- CaSO₄·2H₂O
- Chemical class
- Sulfate
- Varieties
- Selenite
- Also known as
- Selenite (transparent variety), Alabaster (fine-grained), Satin spar (fibrous)
Crystallography
- Crystal system
- Monoclinic
- Habits
- Tabular, Prismatic, Fibrous, Massive
- Fracture
- Splintery
Physical properties
- Mohs hardness
- 2
- Density
- 2.32 g/cm³
- Luster
- Vitreous, Silky, Pearly
- Colors
- colorless, white, yellow, pink, gray
- Streak
- white
- Transparency
- Transparent, Translucent
Geology
- Origins
- Sedimentary
- Host rocks
- Limestone and chalk, Sandstone, shale and clay, Salt beds
- Associated minerals
- Halite, Calcite, Anhydrite, Sulfur
- Found in
- Rock gypsum, Rock salt, Evaporite deposit
- Geography
- worldwide
Classification
- Rarity
- Common
- Gem quality
- No
Sources
- M. Pasero and others, IMA Commission on New Minerals, Nomenclature and Classification, The New IMA List of Minerals, updated September 2026. International Mineralogical Association (CNMNC), 2026.
- Gypsum. Mindat.org (Hudson Institute of Mineralogy).
- J. W. Anthony, R. A. Bideaux, K. W. Bladh, M. C. Nichols, Gypsum. Mineral Data Publishing, Handbook of Mineralogy, 2001.
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