Moonstone
Orthoclase var. Moonstone (Adularia) · Semi-Precious Gemstone
Crystal System
Monoclinic (Tumbled); typically occurs as prismatic crystals or massive, showing Carlsbad twinning.
Mineral Group
Silicates (Subgroup: Tectosilicate; Feldspar group)
Chemical Formula
(K,Na)AlSi3O8
Formation Process
Igneous/Hydrothermal: Formed from cooling magma where orthoclase and albite separate into microscopic alternating layers (exsolution) as they cool.
About This Crystal
Tumbled semi-translucent stone with a vitreous to pearly luster. Exhibits a pale grayish-white body color with visible internal structural banding and billowy light reflection.
Physical Characteristics
Color: White/Grey; Streak: White; Cleavage: Perfect in two directions at nearly 90 degrees; Fracture: Conchoidal to uneven; Specific Gravity: 2.56-2.59; Fluorescence: Weak bluish or orange under UV.
Optical Properties
Refractive Index: 1.518-1.526; Birefringence: 0.005-0.008; Optical Phenomenon: Adularescence (a schiller effect caused by light scattering off internal lamellae).
Hardness & Durability
Origin Region
Notably Sri Lanka (classic blue adularescence), India (multicolor and white), Madagascar, and Myanmar. Found in pegmatites and hydrothermal veins.
Hardness & Durability
Mohs Hardness: 6.0 - 6.5. Fairly brittle with low toughness due to perfect cleavage; susceptible to cracking if dropped or struck.
Care & Maintenance
Avoid ultrasonic and steam cleaners. Clean with warm soapy water and a soft brush. Store separately to prevent scratching from harder stones like quartz or sapphire.
Rarity & Value
Common (commercial grade) to Rare (fine blue transparency). Value is determined by the intensity of the adularescence and transparency. Treatments are uncommon.
Special Characteristics
Adularescence: The 'moonlight' glow that moves across the surface. Can occasionally exhibit chatoyancy (cat's eye) or asterism (four-rayed star).
Lore & History
Historically associated with lunar deities and travelers. In ancient Rome and India, it was believed to be formed from frozen beams of moonlight. Traditionally used for intuition, balance, and the 'Divine Feminine' across various cultures.