mineral
Satin Spar (Satin Spar Gypsum)
Calcium Sulfate Dihydrate (CaSO4·2H2O)
Hardness 2 on the Mohs scale, pearly to silky luster, fibrous structure, perfect cleavage in one direction, white to pearly translucent color, monoclinic crystal system.
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Physical properties
Hardness 2 on the Mohs scale, pearly to silky luster, fibrous structure, perfect cleavage in one direction, white to pearly translucent color, monoclinic crystal system.
Formation & geological history
Forms through the evaporation of mineral-rich water in marine basins, playa lakes, and sedimentary environments.
Uses & applications
Used widely in lapidary work for carved ornaments, palm stones, and decorative wands. Also processed into drywall and plaster of Paris in industry.
Geological facts
Satin Spar is often mislabeled and sold as 'Selenite'. While both are varieties of gypsum, Selenite forms large transparent flat sheets, whereas Satin Spar exhibits a fibrous structure with a silky sheen (chatoyancy).
Field identification & locations
Easily identified by its extremely low hardness (it can be scratched with a fingernail) and its distinctive silky, fibrous appearance that reflects light in a cat's-eye effect. Common in Morocco, Mexico, and the USA.
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