mineral

Selenite (satin spar gypsum)

Gypsum, CaSO₄·2H₂O

AI-generated identification · may be incorrect

Typically colorless to white or pale pink, with a pearly/silky luster and fibrous or bladed crystal structure; Mohs hardness 2, excellent one-direction cleavage, and specific gravity about 2.3. The fibrous striations and soft, easily scratched surface fit satin spar gypsum.

Identified August 26, 2026More mineral →

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Physical properties

Formation & geological history

Forms when evaporating saline water deposits sulfate minerals in sedimentary evaporite beds, commonly from the Permian to Recent eras. Large crystals also grow in cavities and clay-rich deposits through groundwater evaporation.

Uses & applications

Used to make plaster, drywall, cement additives, and soil conditioners; attractive pieces are sold as inexpensive decorative or metaphysical specimens. It is too soft for most jewelry and scratches readily.

Geological facts

“Selenite” properly refers to clear crystalline gypsum, while fibrous varieties are called satin spar; trade names are often used loosely. It can be scratched with a fingernail and dissolves slowly in water.

Field identification & locations

Common in evaporite regions worldwide, notably Mexico, Morocco, Spain, the United States, and Australia. Confirm with a fingernail scratch, white streak, very low weight, and silky parallel fibers; avoid prolonged moisture and abrasion.