mineral
Gypsum (selenite)
Gypsum, CaSO₄·2H₂O; likely a translucent selenite cleavage specimen
AI-generated identification · may be incorrectMohs hardness 2; colorless to white and translucent, with vitreous to pearly luster. Monoclinic crystals; very good cleavage gives thin, sheet-like fragments, and it can be scratched by a fingernail.
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Physical properties
Mohs hardness 2; colorless to white and translucent, with vitreous to pearly luster. Monoclinic crystals; very good cleavage gives thin, sheet-like fragments, and it can be scratched by a fingernail.
Formation & geological history
Forms when calcium- and sulfate-rich water evaporates in sedimentary basins, or through hydration of anhydrite. Gypsum deposits occur from many geological ages, commonly in evaporite layers.
Uses & applications
Used to make plaster, drywall, and cement; clear selenite is also collected and sometimes carved into ornaments.
Geological facts
Gypsum is unusually soft and contains water in its crystal structure; heating it produces plaster of Paris.
Field identification & locations
The white, translucent, layered appearance and easy cleavage are consistent with gypsum, though the photo alone cannot confirm identification. Common deposits occur in evaporite basins worldwide, including the United States, Mexico, and Spain.
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