Mineral

Satin Spar Gypsum

Calcium Sulfate Dihydrate (CaSO4·2H2O)

Hardness: 2 on Mohs scale (can be scratched by a fingernail); Color: Silky white to translucent; Luster: Pearly and chatoyant (cat's-eye effect); Crystal structure: Monoclinic with fibrous growth; Cleavage: Perfect in one direction.

Hardness: 2 on Mohs scale (can be scratched by a fingernail)
Color: Silky white to translucent
Luster: Pearly and chatoyant (cat's-eye effect)

Identified March 21, 2026More mineral →

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Physical properties

Formation & geological history

Formed as an evaporite mineral in sedimentary environments, often resulting from the evaporation of seawater or from the concentration of calcium and sulfate in groundwater. Deposits can range from millions of years old to relatively modern formations.

Uses & applications

Commonly used in plaster of Paris, drywall, and fertilizer. In lapidary arts, it is used for carvings and decorative items, though its softness limits its use in jewelry. Often sold as spiritual 'selenite' wands.

Geological facts

While often marketed as 'Selenite', Satin Spar is technically a fibrous variety of the same mineral family. It is so soft that it is used as the standard index mineral for '2' on the Mohs hardness scale. It can dissolve slowly if left in water for extended periods.

Field identification & locations

Identify in the field by its distinctive silky, fibrous texture and the fact that it can be easily scratched by a fingernail. Found globally in salt flats and clay beds, notably in Morocco, Mexico, and the USA (Utah and New Mexico).

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