mineral
White gypsum (selenite/alabaster variety)
Gypsum, CaSO₄·2H₂O
AI-generated identification · may be incorrectWhite to colorless, pearly or silky luster, with layered/cleavable surfaces; monoclinic crystals. Mohs hardness 2; specific gravity about 2.3.
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Physical properties
White to colorless, pearly or silky luster, with layered/cleavable surfaces; monoclinic crystals. Mohs hardness 2; specific gravity about 2.3.
Formation & geological history
Forms when sulfate-rich water evaporates in sedimentary basins, or through hydration of anhydrite. Gypsum deposits occur across many geological ages; this specimen’s age cannot be determined from the image.
Uses & applications
Used to make plaster, drywall, and cement; clear selenite is also collected and sometimes carved into ornaments.
Geological facts
Gypsum is soft enough to be scratched by a fingernail and can occur as transparent selenite, fibrous satin spar, or fine-grained alabaster.
Field identification & locations
The white, layered appearance is consistent with gypsum, but visual identification is uncertain; confirm with a fingernail scratch and avoid wet testing, as gypsum is slightly water-soluble. Common in evaporite deposits worldwide.
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Calcium sulfate dihydrate (CaSO4·2H2O)
Mineral