mineral

Satin Spar (often marketed as Selenite)

Fibrous Gypsum (Calcium Sulfate Dihydrate) - CaSO4·2H2O

Hardness: 2 on Mohs scale (can be scratched by a fingernail). Color: White or pearly. Luster: Silky or pearlescent. Crystal structure: Monoclinic, habit is fibrous or columnar. Cleavage: Perfect in one direction. Specific Gravity: 2.3.

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

Identified March 16, 2026More mineral →

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Physical properties

Formation & geological history

Formed in sedimentary environments through the evaporation of saline water (evaporite) in ancient lake beds or seafloors. It can also form as a precipitate in hot springs or volcanic vapors. Most commercial deposits date to the Permian or Triassic periods.

Uses & applications

Used primarily for metaphysical purposes, ornamental carvings, and palm stones. Industrially, gypsum is essential for plaster of paris, drywall (sheetrock), and as a soil conditioner in agriculture.

Geological facts

While commonly sold as 'Selenite,' true Selenite is transparent and platy, whereas this specimen is 'Satin Spar,' which is fibrous. It is so soft that it is actually warm to the touch because it is a poor conductor of heat.

Field identification & locations

Identify in the field by its extreme softness and its chatoyancy (cat's-eye effect) when light reflects off the fibrous parallel crystals. Common locations include Morocco, Mexico (Naica Mine), and the USA (Utah and New Mexico). It should never be soaked in water as it can dissolve over time.

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