mineral

Selenite (Satin Spar)

Gypsum (CaSO4·2H2O)

Hardness: 2 on Mohs scale (can be scratched by a fingernail); Color: White to colorless; Luster: Pearly or silky (satin spar variety); Crystal Structure: Monoclinic; Cleavage: Perfect in one direction, yielding thin sheets.

Hardness: 2 on Mohs scale (can be scratched by a fingernail)
Color: White to colorless
Luster: Pearly or silky (satin spar variety)

Identified May 1, 2026More mineral →

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Physical properties

Formation & geological history

Formed as an evaporite mineral in sedimentary environments such as saline lakes, lagoons, and caves when mineral-rich water evaporates. It can form throughout various geological eras.

Uses & applications

Used in the manufacture of drywall (plasterboard), cement, and plaster of Paris. In its mineral form, it is highly popular for decorative lamps, carvings, and metaphysical collecting.

Geological facts

The giant crystals in the 'Cave of the Crystals' in Naica, Mexico, are actually selenite/gypsum, reaching up to 39 feet in length. The name 'selenite' comes from the Greek word 'selēnē' for Moon.

Field identification & locations

Identify by its extreme softness (scratchable with a fingernail) and fibrous, silky appearance. Commonly found in Morocco, Mexico, and the USA. Collectors should avoid getting it wet as it can slowly dissolve or lose its luster.