mineral
Gypsum (likely selenite/alabaster)
Gypsum, CaSO₄·2H₂O
AI-generated identification · may be incorrectWhite to colorless, translucent, with a pearly or vitreous luster and conspicuous cleavage; monoclinic crystals. Mohs hardness 2; specific gravity about 2.3. The photo shows a small white, layered-looking fragment, but does not permit a firm variety identification.
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Physical properties
White to colorless, translucent, with a pearly or vitreous luster and conspicuous cleavage; monoclinic crystals. Mohs hardness 2; specific gravity about 2.3. The photo shows a small white, layered-looking fragment, but does not permit a firm variety identification.
Formation & geological history
Forms when calcium- and sulfate-rich water evaporates in sedimentary basins, or through hydration of anhydrite. Gypsum deposits range from modern to hundreds of millions of years old.
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 be identified by that test, though the specimen may crumble.
Field identification & locations
Common in evaporite deposits worldwide, including large deposits in the United States, Mexico, and Spain. Check for softness and a white streak; value depends on size, clarity, and crystal form.
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