mineral

Moonstone (Variety of Orthoclase Feldspar)

KAlSi3O8 (Potassium Aluminum Silicate)

Hardness: 6.0-6.5 on Mohs scale; Color: Colorless to white/creamy with a blue or white adularescence (sheen); Luster: Vitreous to pearly; Crystal Structure: Monoclinic; Cleavage: Two directions at 90 degrees; Specific Gravity: 2.56-2.59.

Hardness: 6
Luster: Vitreous to pearly

Identified March 14, 2026More mineral →

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Physical properties

Formation & geological history

Formed in plutonic igneous rocks (granites and pegmatites). The characteristic 'glow' is caused by adularescence—the light scattering off internal layers of alternating orthoclase and albite feldspar that separated during cooling.

Uses & applications

Primarily used as a gemstone in jewelry (cabochons, beads, and rings). Historically used in amulets and decorative art, particularly during the Art Nouveau period.

Geological facts

Ancient Romans theorized that moonstone was formed from frozen rays of moonlight. It is the Florida State Gemstone (commemorating the Moon landings), despite not being naturally found in high quantities there.

Field identification & locations

Identify by its 'billowy' light effect (adularescence) that moves across the surface when turned. Common locations include Sri Lanka (known for blue sheen), India, Myanmar, Madagascar, and the United States (New Mexico/Virginia).

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