mineral

Satin Spar (Selenite)

Calcium sulfate dihydrate (CaSO4·2H2O)

Hardness: 2 (can be scratched with a fingernail); Color: Pearly white to translucent; Luster: Silky or pearly; Crystal Structure: Monoclinic (fibrous); Cleavage: Perfect; Specific Gravity: 2.3

Hardness: 2 (can be scratched with a fingernail)
Color: Pearly white to translucent
Luster: Silky or pearly

Identified May 29, 2026More mineral →

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Physical properties

Hardness: 2 (can be scratched with a fingernail); Color: Pearly white to translucent; Luster: Silky or pearly; Crystal Structure: Monoclinic (fibrous); Cleavage: Perfect; Specific Gravity: 2.3

Formation & geological history

Formed in evaporite environments where sea water or saline lake water evaporates. It can also form through the oxidation of sulfides in hydrothermal veins.

Uses & applications

Used in gypsum wallboard (drywall), plaster of Paris, soil conditioners, and as a popular ornamental stone for carvings and metaphysical collections.

Geological facts

Satin spar is often confused with 'true' Selenite, which is the transparent, plate-like variety of gypsum. It is famous for its fiber-optic qualities, where light travels along the length of the internal fibers.

Field identification & locations

Identify by its extreme softness and distinctive silky, fibrous appearance. Look for it in sedimentary basins and arid regions such as Morocco or the Southwestern USA.

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