mineral
Fibrous gypsum (selenite/satin spar)
Gypsum, CaSO₄·2H₂O; fibrous variety
AI-generated identification · may be incorrectLikely gypsum with tan-brown iron-oxide staining and a fibrous, splintery texture. Gypsum has Mohs hardness 2, vitreous to silky luster, monoclinic crystals, and perfect cleavage; the image alone cannot confirm the identification.
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Physical properties
Likely gypsum with tan-brown iron-oxide staining and a fibrous, splintery texture. Gypsum has Mohs hardness 2, vitreous to silky luster, monoclinic crystals, and perfect cleavage; the image alone cannot confirm the identification.
Formation & geological history
Forms when sulfate-rich water evaporates in sedimentary basins, or in veins and cavities; deposits range from recent to hundreds of millions of years old.
Uses & applications
Gypsum is used to make plaster, drywall, and cement; attractive fibrous pieces are collected and sometimes cut as decorative stone.
Geological facts
Gypsum is soft enough to scratch with a fingernail and can be scratched by a copper coin.
Field identification & locations
Check for softness, a white streak, and a silky sheen along fibers; common in evaporite deposits worldwide, including Spain, Mexico, and the United States. The brown color may be surface staining.
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