mineral

Moonstone

Orthoclase Feldspar ((K,Na)AlSi3O8)

Hardness: 6.0-6.5 (Mohs scale), Color: Colorless to white with blue/white adularescence, Luster: Vitreous to pearly, Crystal Structure: Monoclinic, Cleavage: Perfect in two directions.

Hardness: 6

Identified April 12, 2026More mineral →

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Physical properties

Hardness: 6.0-6.5 (Mohs scale), Color: Colorless to white with blue/white adularescence, Luster: Vitreous to pearly, Crystal Structure: Monoclinic, Cleavage: Perfect in two directions.

Formation & geological history

Forms in igneous and metamorphic rocks through the cooling of magma. As it cools, the intergrowth of orthoclase and albite separates into stacked, alternating layers.

Uses & applications

Primarily used as a gemstone in jewelry (rings, pendants, earrings), and as a collector's specimen for its unique optical properties.

Geological facts

The optical phenomenon 'adularescence' is caused by light scattering between microscopic layers of different feldspar minerals. In Ancient Rome, it was believed that moonstones were formed from frozen rays of moonlight.

Field identification & locations

Look for the characteristic internal blue or white glow when the stone is rotated under light. Commonly found in Sri Lanka, India, Myanmar, and Madagascar. Collectors should look for 'Blue Moonstones' which have the highest clarity and strongest blue sheen.