mineral
Selenite gypsum
Gypsum, CaSO₄·2H₂O (selenite variety)
AI-generated identification · may be incorrectWhite, translucent, pearly to vitreous, with prominent sheet-like cleavage and fibrous growth lines; Mohs hardness 2, monoclinic crystal structure, specific gravity about 2.3. The specimen appears to be a naturally formed or lightly shaped selenite fragment.
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Physical properties
White, translucent, pearly to vitreous, with prominent sheet-like cleavage and fibrous growth lines; Mohs hardness 2, monoclinic crystal structure, specific gravity about 2.3. The specimen appears to be a naturally formed or lightly shaped selenite fragment.
Formation & geological history
Forms when evaporating saline or groundwater precipitates calcium sulfate, commonly in sedimentary evaporite beds, caves, and clay-rich deposits. Gypsum deposits range from recent to hundreds of millions of years old.
Uses & applications
Used to manufacture plaster, drywall, cement, and soil amendments; clear selenite is also collected and used decoratively or in crystal displays. It is too soft for durable jewelry.
Geological facts
Selenite can be scratched easily with a fingernail and may split into thin sheets along cleavage planes. It is not the same mineral as satin spar or desert rose, though all are gypsum varieties.
Field identification & locations
Identify it by its very low hardness, light weight, white translucency, and perfect cleavage; a fingernail should leave a mark. Common localities include Mexico, Morocco, Spain, the United States, and Australia.
