mineral

Selenite (satin-spar gypsum)

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

AI-generated identification · may be incorrect

Pale, translucent white with silky, lengthwise striations and a vitreous-to-silky luster. Mohs hardness 2; monoclinic crystals, perfect cleavage in one direction, and specific gravity about 2.3.

Identified September 28, 2026More mineral →

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Physical properties

Pale, translucent white with silky, lengthwise striations and a vitreous-to-silky luster. Mohs hardness 2; monoclinic crystals, perfect cleavage in one direction, and specific gravity about 2.3.

Formation & geological history

Forms when calcium-sulfate-rich water evaporates in sedimentary basins, caves, or arid settings; the mineral can range from recent deposits to ancient evaporites. The image is consistent with a cut or shaped satin-spar specimen.

Uses & applications

Used for collecting, decoration, and carvings; gypsum is also processed for plaster, drywall, and cement. This soft specimen is not suitable for durable jewelry.

Geological facts

Gypsum is soft enough to scratch with a fingernail and may dissolve slowly in water. “Selenite” is a trade name often applied broadly to clear or translucent gypsum.

Field identification & locations

Look for softness, pale color, and parallel fibrous striations; avoid prolonged water exposure and scratching. Common deposits occur in evaporite regions worldwide, including Mexico, the United States, and Morocco.