mineral

Selenite (Satin Spar)

Gypsum (CaSO4·2H2O)

Hardness: 2 on Mohs scale; Color: Pearly white/translucent; Luster: Silky to vitreous; Crystal Structure: Monoclinic; Cleavage: Perfect; Specific Gravity: 2.3

Hardness: 2 on Mohs scale
Color: Pearly white/translucent
Luster: Silky to vitreous

Identified July 8, 2026More mineral →

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Physical properties

Hardness: 2 on Mohs scale; Color: Pearly white/translucent; Luster: Silky to vitreous; Crystal Structure: Monoclinic; Cleavage: Perfect; Specific Gravity: 2.3

Formation & geological history

Formed as an evaporite mineral in sedimentary environments, often from the evaporation of ancient seawater in closed basins or through the hydration of anhydrite.

Uses & applications

Used in ornamental carvings, metaphysical practices, plaster of Paris production, and as a soil conditioner in agriculture.

Geological facts

Selenite is named after the Greek word 'selene' meaning moon, due to its soft moon-like glow. The Naica Mine of Chihuahua, Mexico, contains giant selenite crystals measuring over 30 feet long.

Field identification & locations

Identify by its extreme softness (can be scratched by a fingernail) and fibrous 'cat's eye' chatoyancy. Common in Morocco, Mexico, and the USA. Collectors should keep it dry as it can slightly dissolve over long exposure to water.