mineral

Satin Spar (Selenite)

Gypsum (CaSO4·2H2O)

Hardness: 2 on Mohs scale (can be scratched by a fingernail); Color: White to pearly; Luster: Silky or pearlescent; Crystal Structure: Monoclinic (fibrous habit); Cleavage: Perfect; Specific Gravity: 2.3

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

Identified April 28, 2026More mineral →

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Physical properties

Formation & geological history

Formed in evaporite deposits where saline water evaporates, or as a secondary mineral in sedimentary rocks and around volcanic fumaroles. It can form in various geological ages ranging from millions of years ago to modern formations.

Uses & applications

Used in the manufacture of drywall (gypsum), plaster of Paris, and soil conditioners. In this polished form (sphere), it is primarily used for home decor, meditation, and by mineral collectors.

Geological facts

Satin spar is often confused with 'true' Selenite, which is transparent. The fibrous structure of satin spar creates a 'cat's eye' or chatoyancy effect when light hits it. It is water-soluble over long periods of time.

Field identification & locations

Identify by its extreme softness (scratchable with a nail) and the distinct silky, parallel fibrous texture. Common locations include Morocco, Mexico, and the United States (Utah/New Mexico). Don't soak it in water as it can dissolve or lose its luster.