mineral

Moonstone

Adularia (Potassium Aluminum Silicate, KAlSi3O8)

Hardness: 6.0-6.5 on Mohs scale; Color: Colorless to white/gray with blue or white schiller (flash); Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect in two directions; Specific gravity: 2.56-2.59

Hardness: 6
Color: Colorless to white/gray with blue or white schiller (flash)
Luster: Vitreous to pearly

Identified March 25, 2026More mineral →

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Physical properties

Formation & geological history

Formed in igneous and metamorphic rocks (specifically pegmatites). It is composed of two feldspar species, orthoclase and albite, which intergrow in thin layers. As the mineral cools, these layers separate, creating the optical phenomenon called adularescence.

Uses & applications

Primarily used in jewelry making (cabochons, rings, pendants) and as a popular specimen for crystal collecting and metaphysical practices.

Geological facts

Ancient Romans and Greeks theorized that moonstones were created from solidified rays of the moon. It is the Florida State Gemstone (commemorating the Apollo moon landings) and is a traditional birthstone for June.

Field identification & locations

Identify in the field by its characteristic 'blue flash' or pearly sheen when rotated under light. Common locations include Sri Lanka, India, Myanmar, and Madagascar. Look for a feldspar-like luster and distinct cleavage planes in river gravels or pegmatite veins.

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