mineral

Gypsum (Satin Spar variety)

Calcium Sulfate Dihydrate (CaSO4·2H2O)

AI-generated identification · may be incorrect

Hardness: 2 (can be scratched by a fingernail); Color: white to pearly/translucent; Luster: silky or pearly; Crystal Structure: Monoclinic; Cleavage: perfect in one direction; Specific gravity: 2.3

Hardness: 2 (can be scratched by a fingernail)
Color: white to pearly/translucent
Luster: silky or pearly

Identified July 1, 2026More mineral →

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Physical properties

Hardness: 2 (can be scratched by a fingernail); Color: white to pearly/translucent; Luster: silky or pearly; Crystal Structure: Monoclinic; Cleavage: perfect in one direction; Specific gravity: 2.3

Formation & geological history

Formed as an evaporite mineral in sedimentary environments, typically from the evaporation of seawater in massive basins. It can also form through the hydration of anhydrite or the oxidation of sulfides.

Uses & applications

Primary component of drywall (plasterboard), plaster of Paris, and fertilizer. Used in the production of cement and occasionally carved into decorative items.

Geological facts

Gypsum is the standard for a hardness of 2 on the Mohs scale. Huge crystals of a related variety, Selenite, have been found in Mexico's Cave of the Crystals reaching lengths of nearly 40 feet.

Field identification & locations

Identify in the field by its extreme softness (scratches with a fingernail) and silky, fibrous appearance. Commonly found in desert regions or near saline lakes.