mineral

Satin Spar (Gypsum)

Calcium Sulfate Dihydrate (CaSO4·2H2O)

Hardness: 2 on Mohs scale (can be scratched by a fingernail). Color: White to pearly. Luster: Silky/Satin-like. Crystal Structure: Monoclinic, often fibrous. Cleavage: Perfect in one direction.

Hardness: 2 on Mohs scale (can be scratched by a fingernail)
Color: White to pearly
Luster: Silky/Satin-like

Identified May 28, 2026More mineral →

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Physical properties

Hardness: 2 on Mohs scale (can be scratched by a fingernail). Color: White to pearly. Luster: Silky/Satin-like. Crystal Structure: Monoclinic, often fibrous. Cleavage: Perfect in one direction.

Formation & geological history

Formed as an evaporite mineral in sedimentary environments, often resulting from the evaporation of seawater or in hydrothermal veins and hot springs.

Uses & applications

Used in the manufacture of plaster of Paris, drywall, cement, and as a soil conditioner. Fibrous varieties like this are also popular as ornamental stones and in metaphysical collections.

Geological facts

Satin Spar is a fibrous variety of gypsum. It is often confused with Selenite, which is the transparent crystalline variety, and Alabaster, which is the massive fine-grained variety.

Field identification & locations

Identify it by its extreme softness (scratches with a fingernail) and its distinctive fibrous, silky appearance. Commonly found in desert regions or near volcanic fumaroles.

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