mineral

Moonstone (Adularia)

Potassium aluminum silicate (KAlSi3O8)

Hardness: 6-6.5 on Mohs scale; Color: Colorless to white with blue/white sheen; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Specific gravity: 2.56-2.59

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

Identified June 8, 2026More mineral →

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Physical properties

Hardness: 6-6.5 on Mohs scale; Color: Colorless to white with blue/white sheen; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Specific gravity: 2.56-2.59

Formation & geological history

Formed in igneous and metamorphic rocks, specifically in pegmatites. The characteristic schiller effect (adularescence) is caused by the intergrowth of two types of feldspar, orthoclase and albite, in thin layers.

Uses & applications

Primarily used in jewelry as gemstones, cabochons, and decorative carvings. It is the birthstone for June.

Geological facts

Ancient Romans believed moonstone was formed from frozen beams of moonlight. It is known for its unique optical phenomenon called adularescence, which creates a 'billowy' light that moves across the stone.

Field identification & locations

Identify by its characteristic blue or white glow when moved under a light. Frequently found in Sri Lanka, India, Myanmar, and Madagascar. Look for the layered internal structure.

Other mineral specimens

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Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Schist

Metamorphic

Epidote

Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)

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Nephrite Jade

Nephrite

Mineral/Rock

Banded Gneiss (River Rock/Pebble)

Gneiss (specifically a banded variety often found as a river rock)

Metamorphic Rock

Biotite Schist

Biotite-rich Schist [K(Mg,Fe)3AlSi3O10(F,OH)2]

metamorphic