mineral

Satin Spar (commonly sold as Selenite)

Hydrous Calcium Sulfate (CaSO4·2H2O)

Hardness: 2 on Mohs scale (can be scratched by a fingernail). Color: Pearly white with a silky sheen. Luster: Vitreous to pearly/silky. Crystal structure: Monoclinic; often fibrous or columnar. Cleavage: Perfect and easy to flake. Specific gravity: 2.3.

Hardness: 2 on Mohs scale (can be scratched by a fingernail)
Color: Pearly white with a silky sheen
Luster: Vitreous to pearly/silky

Identified March 29, 2026More mineral →

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Physical properties

Formation & geological history

Formed as an evaporite mineral from the evaporation of seawater in prehistoric marine basins. Deposits can range from millions of years old to relatively modern. Typically found in sedimentary environments and clay beds.

Uses & applications

Used widely for decorative carvings, holistic healing crystals, and ornaments. Industrially, gypsum is essential for making drywall (plasterboard), cement, and as a soil conditioner in agriculture.

Geological facts

While commonly sold as 'Selenite,' true Selenite is transparent and crystalline; this fibrous variety is scientifically 'Satin Spar.' It is water-soluble over long periods of time, so it should never be soaked in water.

Field identification & locations

Identify in the field by its extreme softness (scratches with a nail) and fibrous texture that chatoyantly reflects light like a cat's eye. Found in abundance in Morocco, Mexico, and the USA (Utah/New Mexico). Collect by hand as it is very fragile.

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