mineral

Moonstone

Orthoclase Feldspar ((K,Na)AlSi3O8)

Hardness: 6.0–6.5 Mohs; Color: Colorless to white with blue/white adularescence; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect in two directions.

Hardness: 6
Color: Colorless to white with blue/white adularescence
Luster: Vitreous to pearly

Identified March 31, 2026More mineral →

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Physical properties

Hardness: 6.0–6.5 Mohs; Color: Colorless to white with blue/white adularescence; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect in two directions.

Formation & geological history

Formed in igneous and metamorphic rocks, specifically pegmatites. The characteristic glow (adularescence) is caused by the intergrowth of two types of feldspar (orthoclase and albite) that separate as the mineral cools.

Uses & applications

Primarily used in jewelry (cabochons, rings, pendants) and as a collector gemstone. Historically used in amulets and decorative art.

Geological facts

Ancient Romans believed moonstone was formed from frozen beams of moonlight. It is the Florida State Gemstone (commemorating the moon landings) and a traditional birthstone for June.

Field identification & locations

Identify by its unique 'billowy' light effect (adularescence) that moves across the surface. Found commonly in Sri Lanka, India, Madagascar, and Myanmar. Use a scratch test (harder than glass) but be careful of its brittle cleavage.