mineral

Moonstone

Orthoclase Feldspar (KAlSi3O8)

Hardness: 6.0-6.5 on Mohs scale; Color: peach, tan, or creamy pink with adularescence; Luster: vitreous to pearly; Crystal Structure: Monoclinic; Cleavage: two directions at nearly 90 degrees; Specific Gravity: 2.56-2.59.

Hardness: 6
Color: peach, tan, or creamy pink with adularescence
Luster: vitreous to pearly

Identified May 25, 2026More mineral →

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Physical properties

Formation & geological history

Formed in igneous and metamorphic rocks through the cooling of silica-rich magmas or through hydrothermal activity. The distinct optical effect (adularescence) is caused by the intergrowth of two types of feldspar (orthoclase and albite) that separate as the mineral cools.

Uses & applications

A popular gemstone used extensively in jewelry such as rings, necklaces, and earrings; also valued by mineral collectors for its unique optical properties and metaphysical associations.

Geological facts

Ancient Romans believed moonstone was formed from frozen beams of moonlight. The play of light, known as adularescence, appears to billow across the stone’s surface like moonlight through thin clouds.

Field identification & locations

Identify in the field by its distinct waxy luster and internal 'glow' when rotated under light. Major deposits are found in Sri Lanka, India, Myanmar, and Madagascar. Collectors should look for stones with a strong, centered schiller effect.