mineral
Likely selenite (gypsum) crystal
Gypsum, CaSO₄·2H₂O; variety likely satin spar or fibrous selenite
AI-generated identification · may be incorrectVery pale gray-white, translucent, pearly to silky luster, and strongly fibrous/elongated crystal structure. Mohs hardness 2, perfect cleavage in one direction, and low specific gravity (~2.3); the thin form appears naturally splintery rather than glassy.
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Physical properties
Very pale gray-white, translucent, pearly to silky luster, and strongly fibrous/elongated crystal structure. Mohs hardness 2, perfect cleavage in one direction, and low specific gravity (~2.3); the thin form appears naturally splintery rather than glassy.
Formation & geological history
Gypsum forms when saline or evaporitic waters evaporate, commonly in sedimentary basins, caves, and hydrothermal settings. Deposits range from ancient evaporites to modern cave growth; the image alone cannot establish a precise age.
Uses & applications
Used in drywall, plaster, cement, fertilizer, and soil amendments; clear selenite is also sold as a decorative and collecting mineral. This specimen is likely low-value unless unusually transparent, large, or aesthetically distinctive.
Geological facts
Selenite is a transparent crystalline variety of gypsum, while satin spar is the fibrous variety; trade names are often used loosely. Gypsum can be scratched easily with a fingernail and may form delicate spear-, blade-, or rosette-shaped crystals.
Field identification & locations
Common localities include Mexico, Morocco, Spain, the United States, and evaporite regions worldwide. Test cautiously with a fingernail: gypsum scratches readily and should not be confused with harder calcite or glass.
