Satin Spar (Selenite Gypsum Sphere)

Physical Properties

Hardness: 2 on Mohs scale (very soft, scratchable by a fingernail); Color: Pearly white to translucent; Luster: Silky or pearly; Crystal structure: Monoclinic; Cleavage: Perfect in one direction.

Formation & Geological History

Formed as an evaporite mineral in sedimentary basins or around hot springs and volcanic vents. It crystallizes from brine as water evaporates over millions of years, often in arid alkaline environments.

Uses & Applications

Commonly used for ornamental purposes like carved spheres, wands, and lamps. Industrially, gypsum is the primary component of plaster, drywall (wallboard), and fertilizer.

Geological Facts

Satin spar is often confused with 'true' Selenite, which is the flat, clear crystalline version of gypsum. Despite its name, it does not contain selenium. The fibers of satin spar give it a 'cat's eye' or chatoyant effect.

Field Identification & Locations

Identify in the field by its extreme softness—it can be easily scratched by a fingernail—and its fibrous, silky appearance. Commonly found in Morocco, Mexico (Naica Mine), and the USA (Utah and New Mexico).

Identified on: 4/28/2026

Mode: Standard