Satin Spar (Selenite)

Physical Properties

Hardness: 2 (can be scratched with a fingernail); Color: Translucent white with a pearly or silky sheen; Luster: Silky; Crystal Structure: Monoclinic; Cleavage: Perfect in one direction, causing fibrous appearance; Specific Gravity: 2.3

Formation & Geological History

Formed as an evaporite mineral in sedimentary environments, often resulting from the evaporation of seawater in prehistoric basins or saline lakes. It can be found in layers of sedimentary rock dating back hundreds of millions of years.

Uses & Applications

Used primarily for ornamental purposes like carvings, lamps, and jewelry (though fragile). In industry, gypsum is used in plaster, drywall, and as a soil conditioner in agriculture.

Geological Facts

Satin Spar is a fibrous variety of gypsum. It is often mislabeled simply as 'Selenite,' which technically refers to the clear, transparent variety of gypsum. It is famous for its optical properties where it can reflect light like a fiber-optic cable.

Field Identification & Locations

Identify it by its extreme softness (the fingernail test) and its characteristic pearly, fibrous chatoyancy when turned in the light. Commonly found in Morocco, Mexico, and the USA (Utah and New Mexico). Useful for beginners due to ease of identification.

Identified on: 4/13/2026

Mode: Standard