mineral

Selenite (Satin Spar)

Gypsum (CaSO4·2H2O)

Hardness: 2 (easily scratched by a fingernail), Color: White/Translucent, Luster: Pearly to silky (Satin Spar variety), Crystal Structure: Monoclinic, Cleavage: Perfect, Specific Gravity: 2.3

Identified May 9, 2026More mineral →

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Physical properties

Hardness: 2 (easily scratched by a fingernail), Color: White/Translucent, Luster: Pearly to silky (Satin Spar variety), Crystal Structure: Monoclinic, Cleavage: Perfect, Specific Gravity: 2.3

Formation & geological history

Formed as an evaporite mineral in alkaline lake flats, clay beds, and caverns where salt water has evaporated over millions of years. This specimen is the fibrous 'Satin Spar' variety of Gypsum.

Uses & applications

Used in the manufacture of drywall (plasterboard), plaster of Paris, soil conditioners, and as decorative carvings, wands, and tower specimens for collectors.

Geological facts

The name Selenite comes from the Greek word 'selene' meaning 'moon,' referring to its moon-like glow. The world's largest crystals ever found are Selenite crystals in the Naica Mine of Chihuahua, Mexico.

Field identification & locations

Identifiable by its extreme softness (scratched by a nail) and fibrous optical chatoyancy. Often found in Morocco, USA (Utah/New Mexico), and Mexico. Collectors should avoid water as it can dissolve over time.