Rock Identifier
Moonstone (Orthoclase feldspar, (K,Na)AlSi3O8) — gemstone
gemstone

Moonstone

Orthoclase feldspar, (K,Na)AlSi3O8

Hardness: 6 on the Mohs scale, Color: White, bluish-white, or colorless with a characteristic silvery-blue sheen (adularescence), Luster: Vitreous to pearly, Crystal structure: Monoclinic, Cleavage: Perfect in two directions, Specific gravity: 2.56-2.58

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Physical properties

Hardness: 6 on the Mohs scale, Color: White, bluish-white, or colorless with a characteristic silvery-blue sheen (adularescence), Luster: Vitreous to pearly, Crystal structure: Monoclinic, Cleavage: Perfect in two directions, Specific gravity: 2.56-2.58

Formation & geological history

Forms in igneous rocks like granites and pegmatites, as well as in hydrothermal veins, as potassium-rich feldspar cools and unmixes into alternating microscopic layers of orthoclase and albite.

Uses & applications

Used primarily in jewelry making for rings, earrings, necklaces, and as an ornamental gemstone.

Geological facts

Moonstone gets its shimmering optical phenomenon, known as adularescence, from light scattering between microscopic layers of different feldspar minerals within the stone.

Field identification & locations

Identified easily by its characteristic floating blue or white sheen under light. Commonly sourced from Sri Lanka, India, Madagascar, and Myanmar.

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