mineral

Satin Spar (Gypsum)

Calcium Sulfate Dihydrate (CaSO4·2H2O)

AI-generated identification · may be incorrect

Hardness: 2 on Mohs scale; Color: White to pearly; Luster: Silky to pearly; Crystal structure: Monoclinic; Cleavage: Perfect in one direction; Specific gravity: 2.3

Hardness: 2 on Mohs scale
Color: White to pearly
Luster: Silky to pearly

Identified July 3, 2026More mineral →

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Physical properties

Hardness: 2 on Mohs scale; Color: White to pearly; Luster: Silky to pearly; Crystal structure: Monoclinic; Cleavage: Perfect in one direction; Specific gravity: 2.3

Formation & geological history

Formed through the evaporation of seawater in massive prehistoric basins (evaporite) or by the hydration of anhydrite. This fibrous variety often forms in veins.

Uses & applications

Commonly used for ornamental carvings, palm stones, and decorative charging plates. The massive form is used in making plaster of Paris and drywall.

Geological facts

Satin spar is often mislabeled as 'Selenite' in the commercial market. While both are gypsum, selenite strictly refers to the transparent crystal form, while satin spar is the fibrous form.

Field identification & locations

Identifiable by its distinct silky luster and ability to be scratched by a fingernail. It should be kept away from water as it can dissolve or lose its luster over time.