mineral

Satin Spar (Selenite)

Gypsum (Calcium Sulfate Dihydrate) - CaSO4·2H2O

Hardness: 2 on Mohs scale (can be scratched by a fingernail). Color: White/Translucent. Luster: Pearly to silky (chatoyancy). Crystal structure: Monoclinic.

Hardness: 2 on Mohs scale (can be scratched by a fingernail)
Color: White/Translucent
Luster: Pearly to silky (chatoyancy)

Identified March 21, 2026More mineral →

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Physical properties

Hardness: 2 on Mohs scale (can be scratched by a fingernail). Color: White/Translucent. Luster: Pearly to silky (chatoyancy). Crystal structure: Monoclinic.

Formation & geological history

Formed as an evaporite mineral in sedimentary environments, typically where saltwater has evaporated. Occurs in massive beds and as veins in mudstones.

Uses & applications

Commonly used in plaster of paris, drywall (gypsum board), soil conditioners, and as decorative carvings or 'metaphysical' crystals.

Geological facts

Satin spar is often mislabeled simply as 'selenite', which is technically the transparent plate-like variety of gypsum. It exhibits a fiber-optic effect where light travels along its internal fibrous structure.

Field identification & locations

Identify by its extreme softness and silky, fibrous sheen. Common locations include Morocco, Mexico, and the USA (Utah). Collectors should keep it away from water as it is slightly soluble.

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