mineral

Moonstone (Feldspar)

Orthoclase or Oligoclase (KAlSi3O8)

Hardness: 6.0-6.5 on Mohs scale; Color: Creamy white, translucent; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect in two directions at nearly 90 degrees; Specific gravity: 2.56-2.59; Optical effect: Adularescence (inner glow).

Hardness: 6
Color: Creamy white, translucent
Luster: Vitreous to pearly

Identified March 8, 2026More mineral →

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Physical properties

Formation & geological history

Formed in igneous or metamorphic rocks through slow cooling where two types of feldspar (orthoclase and albite) intermix and then separate into layers; found in pegmatite veins and metamorphic deposits.

Uses & applications

Primarily used in jewelry (cabochons) and as a collector's mineral; associated with metaphysical beliefs and birthstones.

Geological facts

Ancient Romans believed moonstone was formed from frozen moonlight. The blue sheen effect, called adularescence, is caused by light scattering between thin microscopic layers of feldspar.

Field identification & locations

Identify in the field by the high hardness (scratches glass with difficulty but can be scratched by quartz) and the signature internal white-to-blue light reflection when tilted. Commonly found in India, Sri Lanka, and parts of the United States (New Mexico, Virginia).

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