mineral

Selenite (gypsum) crystal

Gypsum, CaSO₄·2H₂O; fibrous variety often called satin spar

AI-generated identification · may be incorrect

Colorless to white, translucent, vitreous to pearly/silky luster; hardness 2 Mohs, perfect cleavage in one direction, monoclinic crystals, and specific gravity about 2.3. The long parallel fibers and soft, easily scratched surface are characteristic of satin spar gypsum.

Identified August 30, 2026More mineral →

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Physical properties

Formation & geological history

Forms by evaporation of sulfate-rich seawater or groundwater in sedimentary evaporite basins, commonly during the Permian to Recent. This appears to be a cut or shaped fibrous crystal rather than a natural crystal termination.

Uses & applications

Used for plaster, drywall, cement, soil amendments, and sculpture; clear selenite is popular for mineral collections and spiritual décor, but it is too soft for most jewelry. Avoid prolonged water exposure because gypsum can dissolve or weaken.

Geological facts

The name selenite derives from Selene, the Greek moon goddess, referring to its moonlike pearly sheen. It should not be confused with selenium or moonstone.

Field identification & locations

Common localities include Mexico, Morocco, Spain, the United States, and Canada; large desert specimens are especially associated with Naica, Mexico. Scratch testing with a fingernail, silky fibers, and perfect cleavage help distinguish it from harder quartz.