mineral

Satin Spar (Selenite)

Gypsum (Calcium Sulfate Dihydrate) - CaSO4·2H2O

Hardness: 2 (can be scratched by a fingernail); Color: Colorless to white; Luster: Pearly or silky; Crystal structure: Monoclinic; Cleavage: Perfect; Specific gravity: 2.3

Hardness: 2 (can be scratched by a fingernail)
Color: Colorless to white
Luster: Pearly or silky

Identified April 13, 2026More mineral →

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Physical properties

Hardness: 2 (can be scratched by a fingernail); Color: Colorless to white; Luster: Pearly or silky; Crystal structure: Monoclinic; Cleavage: Perfect; Specific gravity: 2.3

Formation & geological history

Formed in evaporative environments where saline water evaporates, usually in sedimentary deposits such as salt flats or clay beds.

Uses & applications

Used in the manufacture of plaster of Paris, wallboard (drywall), soil fertilizer, and commercially as a metaphysical or ornamental crystal.

Geological facts

Satin spar is often confused with 'true' selenite, which is transparent and plate-like. Satin spar is the fibrous form. It is so soft that it is extremely sensitive to water and will eventually dissolve if soaked.

Field identification & locations

Identify in the field by its extreme softness (can be scratched by a fingernail) and fibrous, silky appearance. Commonly found in Naica (Mexico), Morocco, and the Southwestern US.

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