mineral
Likely gypsum (selenite)
Gypsum — CaSO₄·2H₂O
AI-generated identification · may be incorrectPale gray-white, translucent, with a vitreous to pearly luster and prominent cleavage; gypsum has Mohs hardness 2 and monoclinic crystals. The photo’s small, irregular piece is not diagnostic, so identification is tentative.
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Physical properties
Pale gray-white, translucent, with a vitreous to pearly luster and prominent cleavage; gypsum has Mohs hardness 2 and monoclinic crystals. The photo’s small, irregular piece is not diagnostic, so identification is tentative.
Formation & geological history
Gypsum forms when sulfate-rich water evaporates in sedimentary basins, commonly alongside halite; deposits range from recent 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 scratch with a fingernail, a useful field test; avoid soaking it because it is slightly water-soluble.
Field identification & locations
Common in evaporite deposits worldwide, including the United States, Mexico, and Spain. Check for softness and cleavage, but confirm with additional tests because pale minerals can look similar.
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