Mineral

Gypsum (variety Selenite or Alabaster)

Calcium sulfate dihydrate (CaSO4·2H2O)

AI-generated identification · may be incorrect

Hardness: 2 on Mohs scale (can be scratched by a fingernail). Color: White, colorless, or shades of gray/brown. Luster: Vitreous to pearly. Crystal structure: Monoclinic occurring as crusts or massive aggregates. Specific gravity: 2.3.

Hardness: 2 on Mohs scale (can be scratched by a fingernail)
Color: White, colorless, or shades of gray/brown
Luster: Vitreous to pearly

Identified June 28, 2026More mineral →

Explore Gypsum (variety Selenite or Alabaster) in the encyclopedia →

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Physical properties

Formation & geological history

Formed as an evaporite mineral in sedimentary environments such as saline lakes, coastal pans, and salt flats through the evaporation of mineral-rich water.

Uses & applications

Primary component of drywall (plasterboard), plaster of Paris, and used as a soil conditioner in agriculture. Ornamental varieties are used for carving.

Geological facts

Gypsum is the most common sulfate mineral. The massive white variety is known as alabaster, and the clear crystalline variety is known as selenite. It is very soft and can be easily carved or crushed.

Field identification & locations

Identify in the field by its extreme softness (scratches with a fingernail) and white/tan crust-like appearance on lake beds or desert floors. Commonly found in arid regions like California, Nevada, or White Sands, New Mexico.