mineral

Selenite (satin spar gypsum)

Gypsum, CaSO₄·2H₂O; fibrous variety known as satin spar

AI-generated identification · may be incorrect

Typically colorless to white with silky, pearly luster and long parallel fibers; Mohs hardness 2, monoclinic crystal system, perfect cleavage, specific gravity about 2.3. The image shows a translucent, elongated polished piece consistent with satin spar.

Identified September 29, 2026More mineral →

Explore Selenite (satin spar gypsum) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Forms when calcium-sulfate-rich water evaporates in sedimentary basins, or through hydration of anhydrite; gypsum deposits occur from many geological periods. The exact age and source of this specimen cannot be determined from the image.

Uses & applications

Used for decorative carvings and display; gypsum is also processed for plaster, drywall, and cement. Satin spar is generally too soft for durable jewelry.

Geological facts

Gypsum is soft enough to scratch with a fingernail and can be scratched by a copper coin. Satin spar’s fibrous texture creates its characteristic silky sheen.

Field identification & locations

Look for a soft, pale mineral with parallel fibers and a silky reflection; it is found in evaporite deposits worldwide, including Spain, Mexico, Morocco, and the United States. Avoid soaking it or using harsh cleaners.