mineral

Moonstone

Orthoclase Feldspar (KAlSi3O8)

Hardness: 6.0-6.5 on Mohs scale; Color: Colorless to white, gray, or peach with blue/white adularescence; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect in two directions; Specific gravity: 2.56-2.59

Hardness: 6
Luster: Vitreous to pearly

Identified June 21, 2026More mineral →

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Physical properties

Formation & geological history

Formed in igneous and metamorphic rocks from cooling magma or hydrothermal activity. Its unique glow comes from the intergrowth of two types of feldspar (orthoclase and albite) that separate into thin, alternating layers as the mineral cools.

Uses & applications

Primary use is in jewelry as gemstones (cabs or faceted). Also a popular mineral for metaphysical collecting and historically used as an amulet.

Geological facts

Ancient Romans believed moonstone was formed from frozen drops of moonlight. It is the Florida State Gemstone (honoring the Apollo moon landings) and is known for 'adularescence'—an optical phenomenon that causes a shimmering light to move across the stone.

Field identification & locations

Identify by its distinctive milky blue or white sheen when rotated under light. Commonly found in Sri Lanka, India, Myanmar, Madagascar, and parts of the USA (like New Mexico). To test in the field, look for the 'schiller' effect and scratch resistance (it will scratch glass but be scratched by quartz).