mineral

Satin Spar (Selenite)

Gypsum (Calcium Sulfate Dihydrate) - CaSO4·2H2O

Hardness: 2 on the Mohs scale (can be scratched by a fingernail). Color: White or transparent with a pearly or silky luster. Crystal structure: Monoclinic with long, fibrous parallel crystals. Cleavage: Perfect in one direction. Specific gravity: 2.3.

Hardness: 2 on the Mohs scale (can be scratched by a fingernail)
Color: White or transparent with a pearly or silky luster

Identified March 30, 2026More mineral →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed as an evaporite mineral in sedimentary environments, typically where ancient seawater has evaporated across many geological ages, from the Permian to the present. Often found in clay beds or near hot springs.

Uses & applications

Primarily used for decorative purposes, crystal healing, and as metaphysical 'cleansing' wands. Industrial gypsum is used for drywall, plaster, and as a soil conditioner (fertilizer).

Geological facts

While commonly sold as 'Selenite,' this fibrous variety is technically Satin Spar. True Selenite is transparent and plate-like. It is extremely water-soluble; soaking this specimen in water will cause it to eventually dissolve or lose its luster.

Field identification & locations

Identify in the field by its extreme softness and fibrous, 'cat's eye' silky chatoyancy. It is commonly found in Morocco, Mexico (Naica Mine), and the USA (Utah and New Mexico). Collectors should look for the characteristic 'fiber optic' effect when light passes through the side.

Other mineral specimens

See all

Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Epidote

Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)

metamorphic

Nephrite Jade

Nephrite

Mineral/Rock

Banded Gneiss (River Rock/Pebble)

Gneiss (specifically a banded variety often found as a river rock)

Metamorphic Rock

Green Apatite on Albite

Fluorapatite [Ca5(PO4)3F] on Albite [Na(AlSi3O8)]

mineral

Epidote

Epidote - Ca2(Al2,Fe3+)3(SiO4)3(OH)

mineral