mineral

Satin Spar (Gypsum variety)

Calcium Sulfate Dihydrate (CaSO4·2H2O)

Hardness: 2 on Mohs scale (scratchable by fingernail). Color: White or colorless, often translucent. Luster: Pearly or silky (chatoyant). Crystal structure: Monoclinic, typically fibrous. Cleavage: Perfect in one direction.

Hardness: 2 on Mohs scale (scratchable by fingernail)
Color: White or colorless, often translucent
Luster: Pearly or silky (chatoyant)

Identified March 9, 2026More mineral →

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Physical properties

Formation & geological history

Formed as an evaporite mineral in sedimentary environments, typically from the evaporation of seawater or in hydrothermal veins and hot springs. Can occur in Mesozoic to Cenozoic deposits.

Uses & applications

Used primarily in the manufacture of drywall (plasterboard), cement, and plaster of Paris. In its fibrous form (satin spar), it is popular in the metaphysical community and for making carvings, wands, and decorative items.

Geological facts

Satin Spar is often mislabeled as 'Selenite' in the commercial market. While both are varieties of gypsum, true selenite is transparent and plate-like, while satin spar is fibrous and produces a 'cat's eye' shimmer effect known as chatoyancy.

Field identification & locations

Identify in the field by its extreme softness (can be scratched by a fingernail) and its fibrous, silky luster. Commonly found in Morocco, Mexico, and the USA (Utah/New Mexico). Collectors should avoid getting it wet as it can dissolve or degrade over time.

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