mineral

Satin Spar (Selenite)

Gypsum (CaSO4·2H2O)

Hardness: 2 on Mohs scale (can be scratched by a fingernail). Color: White to pearly cream. Luster: Silky or pearly. Crystal structure: Monoclinic, often fibrous. Cleavage: Perfect in one direction. Specific gravity: 2.3.

Hardness: 2 on Mohs scale (can be scratched by a fingernail)
Color: White to pearly cream
Luster: Silky or pearly

Identified April 19, 2026More mineral →

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Physical properties

Formation & geological history

Formed as an evaporite mineral in sedimentary environments, typically from the evaporation of ancient seawater in lagoons or landlocked basins. Can be found in deposits dating from the Precambrian to Holocene.

Uses & applications

Used primarily for ornamental jewelry, crystal healing, and decorative carvings. Industrial gypsum is used for plaster of Paris, drywall, and soil conditioner.

Geological facts

Satin Spar is a fibrous variety of gypsum often marketed as 'Selenite'. It exhibits a distinct 'cat's eye' effect or chatoyancy due to its parallel fibrous structure. It is extremely soft and can dissolve if soaked in water for long periods.

Field identification & locations

Identify by its 'silky' sheen and extreme softness; if you can scratch it with your fingernail, it is likely a gypsum variety. Often found in desert regions or near salt flats. Collectors should avoid water when cleaning.