Moonstone
Feldspar group, Orthoclase var. Moonstone · Semi-Precious Gemstone
Crystal System
Monoclinic; prismatic habit, often found as massive or blocky crystals
Mineral Group
Silicates (Tectosilicates)
Chemical Formula
KAlSi3O8
Formation Process
Igneous and metamorphic; forms as cooling magma separates into alternating microscopic layers of orthoclase and albite (perthitic intergrowth)
About This Crystal
Rectangular faceted gemstone set in a ring, exhibiting a translucent to adularescent body with a characteristic whitish-blue sheen and subtle internal inclusions
Physical Characteristics
White to colorless body color with a silvery-blue adularescent sheen, white streak, two directions of perfect cleavage at nearly 90 degrees, uneven to conchoidal fracture, specific gravity around 2.56 to 2.58, brittle tenacity
Optical Properties
Biaxial negative with double refraction, refractive index ranging from 1.518 to 1.526, exhibits strong adularescence (schiller effect) caused by light scattering from microscopic albite lamellae
Hardness & Durability
Origin Region
Sri Lanka, India, Madagascar, Myanmar, Australia, and the United States; forms in igneous pegmatites and metamorphic rocks
Hardness & Durability
Mohs hardness of 6 to 6.5, poor to fair toughness due to distinct cleavage planes, sensitive to sharp impacts and sudden thermal shock, moderate wearability for rings if protected by setting
Care & Maintenance
Clean with warm soapy water and a soft brush, avoid ultrasonic and steam cleaners, store separately to prevent scratching by harder stones, sensitive to hydrofluoric acid
Rarity & Value
Common to uncommon depending on the quality of adularescence and body clarity; high-quality specimens with strong blue sheen from Sri Lanka command higher values; typically untreated
Special Characteristics
Exhibits adularescence, a billowy, moon-like sheen caused by the interference of light reflecting between alternating layers of orthoclase and albite feldspar
Lore & History
Historically associated with lunar deities in Roman and Hindu mythology; believed in crystal lore to promote intuition, emotional balance, and new beginnings, though these are traditional beliefs rather than scientific claims