Rock Identifier
Moonstone (Orthoclase feldspar (KAlSi3O8)) — mineral
mineral

Moonstone

Orthoclase feldspar (KAlSi3O8)

Hardness: 6-6.5 on Mohs scale; Color: Colorless to white/gray with adularescence; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect in two directions; Specific gravity: 2.56-2.59

Hardness
6-6
Color
Colorless to white/gray with adularescence
Luster
Vitreous to pearly
Identified More mineral →

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Physical properties

Hardness: 6-6.5 on Mohs scale; Color: Colorless to white/gray with adularescence; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect in two directions; Specific gravity: 2.56-2.59

Formation & geological history

Formed in plutonic igneous rocks (magmatism) and pegmatites. It consists of two feldspar species, orthoclase and albite, that intergrow as the mineral cools, creating an alternating layer structure.

Uses & applications

Primarily used in jewelry as cabochons, carvings, or beads. Also a popular specimen for gemstone collectors and used in holistic practices.

Geological facts

The characteristic 'glow' is called adularescence, caused by light scattering between microscopic layers of feldspar. It is the Florida State Gemstone (commemorating the Moon landing) and is the birthstone for June.

Field identification & locations

Identify by its 'shiller' effect—a milky blue or white light that moves across the surface when rotated. Found commonly in Sri Lanka, India, Myanmar, and Madagascar. In the field, look for a pearly luster and typical feldspar cleavage planes.

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