mineral

Satin Spar (Gypsum)

Calcium Sulfate Dihydrate (CaSO4·2H2O)

Hardness: 2 on Mohs scale (can be scratched by a fingernail). Color: White, pearly, or translucent. Luster: Pearly to silky. Crystal structure: Monoclinic, typically fibrous. Cleavage: Perfect in one direction, yielding thin sheets or fibers.

Hardness: 2 on Mohs scale (can be scratched by a fingernail)
Color: White, pearly, or translucent
Luster: Pearly to silky

Identified March 7, 2026More mineral →

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Physical properties

Formation & geological history

Formed as an evaporite mineral in sedimentary environments, typically where seawater or saline lake water evaporates. It can also form through the hydration of anhydrite or in hydrothermal veins.

Uses & applications

Used in the manufacture of wallboard (drywall), cement, and plaster of Paris. In its fibrous 'satin spar' form, it is popular for ornamental carvings, meditation stones, and metaphysical collecting.

Geological facts

Satin spar is often mislabeled as 'selenite' in the gemstone market; while both are gypsum, selenite is the transparent, plate-like variety, while satin spar is the fibrous, silky variety. It is so soft that it can be easily carved with simple hand tools.

Field identification & locations

Identify in the field by its extreme softness (scratch with a fingernail) and its distinctive silky, fibrous appearance that reflects light in a 'cat's eye' effect. Commonly found in desert regions like Morocco, the USA (Utah/New Mexico), and Mexico.

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