mineral

Satin Spar Selenite

Gypsum (Calcium Sulfate Dihydrate, CaSO4·2H2O)

Hardness: 2 on Mohs scale (can be scratched by a fingernail); Color: Translucent white with a pearly or silky sheen; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect; Specific gravity: 2.3

Hardness: 2 on Mohs scale (can be scratched by a fingernail)
Color: Translucent white with a pearly or silky sheen
Luster: Vitreous to pearly

Identified March 27, 2026More mineral →

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Physical properties

Formation & geological history

Forms primarily as an evaporite mineral in sedimentary environments such as saline lakes, lagoons, and deep-sea basins where calcium-rich waters evaporate. It can also form through the oxidation of sulfides in hydrothermal veins.

Uses & applications

Used in the manufacture of plaster of Paris, drywall (gypsum board), and fertilizers. In the spiritual and mineral collecting communities, it is popular for decorative carvings, palm stones, and wands due to its optical properties.

Geological facts

In its common silky fibrous form, it is known as 'satin spar.' It is so soft that it can be scratched by a human fingernail, which is a primary diagnostic test for identifying it against similar-looking minerals like calcite or quartz.

Field identification & locations

Identify in the field by its characteristic silky luster and extreme softness. It is commonly found in Morocco, Mexico, and the United States (Utah and New Mexico). Collectors should avoid getting it wet, as it is slightly soluble in water over time.

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