mineral

Gypsum (Satin Spar / Alabaster variety)

Calcium Sulfate Dihydrate (CaSO4·2H2O)

Hardness: 2 (can be scratched by a fingernail); Color: Peachy-pink, white, or colorless; Luster: Pearly to vitreous; Crystal Structure: Monoclinic; Cleavage: Perfect in one direction; Specific Gravity: 2.3

Hardness: 2 (can be scratched by a fingernail)
Color: Peachy-pink, white, or colorless
Luster: Pearly to vitreous

Identified June 28, 2026More mineral →

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Physical properties

Formation & geological history

Formed as an evaporite mineral from the evaporation of seawater in massive prehistoric basins or through the hydration of anhydrite. Often found in sedimentary beds associated with limestones and shales.

Uses & applications

Used in the manufacture of drywall (plasterboard), cement, and plaster of Paris. Fine-grained varieties (alabaster) are used for ornamental carvings and sculptures.

Geological facts

Gypsum is the most common sulfate mineral. The massive crystals found in the Cave of the Crystals in Mexico are made of the selenite variety of gypsum.

Field identification & locations

Identify in the field by its extreme softness (the fingernail test) and its characteristic fibrous or massive texture. Commonly found in arid regions like the American Southwest, as seen in the background of the image.

Other mineral specimens

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Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Schist

Metamorphic

Epidote

Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)

metamorphic

Gypsum (variety Selenite or Alabaster)

Calcium sulfate dihydrate (CaSO4·2H2O)

Mineral

Nephrite Jade

Nephrite

Mineral/Rock

Banded Gneiss (River Rock/Pebble)

Gneiss (specifically a banded variety often found as a river rock)

Metamorphic Rock