gemstone

Moonstone (Feldspar)

Orthoclase Feldspar KAlSi3O8 / Albite NaAlSi3O8

Hardness: 6.0-6.5 on the Mohs scale; Color: Milky white to pale green/grey with subtle adularescence (schiller); Luster: Vitreous to pearly; Crystal structure: Monoclinic/Triclinic; Specific gravity: 2.56-2.59

Hardness: 6
Luster: Vitreous to pearly

Identified July 22, 2026More gemstone →

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Physical properties

Formation & geological history

Formed in plutonic igneous rocks (granites, pegmatites) and metamorphic rocks. As the magma cools, orthoclase and albite intergrow in alternating microscopic layers, causing light interference (adularescence).

Uses & applications

Widely used as a gemstone in jewelry (cabochons, beads, rings) and as a decorative mineral specimen for collectors.

Geological facts

The optical effect called adularescence is caused by light scattering between microscopic layers of orthoclase and albite within the crystal structure. It is the state gemstone of Florida.

Field identification & locations

Identified by its distinctive bluish or milky shimmering sheen (adularescence), pearly luster, and feldspar cleavage patterns. Commonly found along gravel beaches and in pegmatite deposits worldwide (e.g., Sri Lanka, India, Myanmar, Brazil, USA).

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