mineral
Likely selenite (gypsum)
Gypsum, CaSO₄·2H₂O; possibly a small satin-spar or selenite specimen
AI-generated identification · may be incorrectPale gray-white with a pearly, silky luster and parallel fibrous or layered appearance. Gypsum has Mohs hardness 2, monoclinic crystals, and perfect cleavage; the photo’s surface texture is consistent with fibrous gypsum.
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Physical properties
Pale gray-white with a pearly, silky luster and parallel fibrous or layered appearance. Gypsum has Mohs hardness 2, monoclinic crystals, and perfect cleavage; the photo’s surface texture is consistent with fibrous gypsum.
Formation & geological history
Gypsum forms when calcium-sulfate-rich water evaporates in sedimentary basins, often in evaporite deposits. Such deposits range from recent to hundreds of millions of years old; the specimen’s age and locality cannot be determined from the image.
Uses & applications
Used to make plaster, drywall, and cement; clear selenite is also collected and sometimes carved for decoration.
Geological facts
Gypsum is soft enough to be scratched with a fingernail and is notably softer than most common minerals.
Field identification & locations
Look for a soft, pale specimen with a silky sheen and parallel fibers; verify by testing an inconspicuous spot with a fingernail. Gypsum occurs worldwide in evaporite deposits, including Spain, Mexico, and the United States.
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Calcium sulfate dihydrate (CaSO4·2H2O)
Mineral