mineral

Selenite (gypsum crystal)

Gypsum, CaSO₄·2H₂O; variety selenite

AI-generated identification · may be incorrect

Likely a translucent-to-white, pearly specimen with excellent cleavage and a flat, bladed crystal habit. Mohs hardness 2, monoclinic crystal system, vitreous-to-silky luster, and low specific gravity (~2.3); it can be scratched easily with a fingernail.

Identified September 8, 2026More mineral →

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Physical properties

Formation & geological history

Forms when evaporating saline waters precipitate calcium sulfate, commonly in sedimentary evaporite basins; some giant crystals formed in caves over thousands to millions of years. The image may also show a cut or shaped gypsum piece.

Uses & applications

Used to make plaster, drywall, cement, and soil amendments; attractive crystals are sold as décor and mineral specimens. It is generally unsuitable for jewelry because it is very soft and water-soluble.

Geological facts

“Selenite” refers to the clear, crystalline variety of gypsum; satin spar is fibrous and alabaster is massive, fine-grained gypsum. Gypsum has two molecules of structural water per formula unit.

Field identification & locations

Identify it by its very low hardness, perfect cleavage, light weight, and tendency to form transparent blades or sheets; avoid soaking or abrasion. Common localities include Mexico, Morocco, Spain, the United States, and Australia.