Satin Spar (Selenite)

Physical Properties

Hardness: 2 (can be scratched by a fingernail); Color: Colorless to white; Luster: Pearly or silky; Crystal structure: Monoclinic; Cleavage: Perfect; Specific gravity: 2.3

Formation & Geological History

Formed in evaporative environments where saline water evaporates, usually in sedimentary deposits such as salt flats or clay beds.

Uses & Applications

Used in the manufacture of plaster of Paris, wallboard (drywall), soil fertilizer, and commercially as a metaphysical or ornamental crystal.

Geological Facts

Satin spar is often confused with 'true' selenite, which is transparent and plate-like. Satin spar is the fibrous form. It is so soft that it is extremely sensitive to water and will eventually dissolve if soaked.

Field Identification & Locations

Identify in the field by its extreme softness (can be scratched by a fingernail) and fibrous, silky appearance. Commonly found in Naica (Mexico), Morocco, and the Southwestern US.

Identified on: 4/13/2026

Mode: Standard