mineral

Satin Spar (commercially called Selenite)

Gypsum (Calcium Sulfate Dihydrate) - CaSO4·2H2O

Hardness: 2 (Mohs scale, can be scratched by a fingernail). Color: White or pearly. Luster: Silky to pearly. Crystal Structure: Monoclinic; fibers occur in long prismatic bundles. Cleavage: Perfect in one direction. Specific Gravity: 2.3.

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

Identified March 18, 2026More mineral →

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Physical properties

Formation & geological history

Formed as an evaporite mineral in sedimentary environments, typically where saltwater or sulfate-rich groundwater evaporates. It can form in ancient lake beds, lagoons, and clay deposits. Massive deposits range from millions of years old to relatively modern formations.

Uses & applications

Primarily used for ornamental purposes, metaphysical carvings (like the knife shown), and interior decor. In bulk industrial form, gypsum is used in drywall, plaster, and as a soil conditioner in agriculture.

Geological facts

While this fibrous variety is commonly marketed as 'Selenite' in the crystal trade, true Selenite is technically transparent and plate-like. This fibrous, silky version is more accurately called Satin Spar. It is water-soluble; soaking this item in water will eventually dissolve or damage the surface.

Field identification & locations

Identify in the field by its extreme softness and distinctive parallel fibrous structure that creates a 'cat's eye' shimmer effect (chatoyancy). It is commonly found in Morocco, Mexico, and various parts of the USA (Utah, Texas). Collectors should look for fiber stability and absence of staining.

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