mineral
Satin Spar (often sold as Selenite)
Gypsum (Calcium Sulfate Dihydrate, CaSO4·2H2O)
Hardness: 2 on Mohs scale (scratchable by a fingernail); Color: White, pearly; Luster: Silky to pearly; Crystal structure: Monoclinic with fibrous habit; Cleavage: Perfect; Specific gravity: 2.3
- Hardness
- 2 on Mohs scale (scratchable by a fingernail)
- Color
- White, pearly
- Luster
- Silky to pearly
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Physical properties
Hardness: 2 on Mohs scale (scratchable by a fingernail); Color: White, pearly; Luster: Silky to pearly; Crystal structure: Monoclinic with fibrous habit; Cleavage: Perfect; Specific gravity: 2.3
Formation & geological history
Formed as an evaporite mineral in sedimentary environments such as saline lakes, lagoons, and caves where sulfate-rich waters evaporate. It can be found in deposits ranging from the Permian to the Holocene.
Uses & applications
Commonly used for ornamental carvings, interior decor, spiritual/metaphysical practices, and as a source of gypsum for plaster of Paris and drywall in industry.
Geological facts
While often marketed as 'Selenite', this fibrous variety is technically 'Satin Spar'. True Selenite is transparent and platy. The Naica Mine in Mexico contains the world's largest gypsum crystals, reaching over 30 feet in length.
Field identification & locations
Identify by its unique fibrous, silky appearance and its extreme softness; it can be scratched easily by a fingernail. Found globally, with massive deposits in Morocco, Mexico, and the USA. Collectors should keep it dry as it is slightly water-soluble.
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