Moonstone
Orthoclase Feldspar var. Moonstone · Semi-Precious Gemstone / Mineral Specimen
Crystal System
Monoclinic; typically occurs in blocky, tabular habits or large cleavage masses
Mineral Group
Silicates; Tectosilicate (Feldspar Group)
Chemical Formula
(K,Na)AlSi3O8 (Potassium Aluminum Silicate)
Formation Process
Igneous/Hydrothermal; forms in pegmatites and deep-seated plutonic rocks where cooling occurs slowly enough for exsolution of orthoclase and albite layers
About This Crystal
A translucent to transparent specimen showing a characteristic pearly to vitreous luster. The color is colorless to silvery-white with internal planes that reflect light, suggesting a layered structure characteristic of feldspars.
Physical Characteristics
Color: Colorless to white; 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 light.
Optical Properties
Refractive Index: 1.518-1.526; Birefringence: 0.005-0.008; Optical Phenomenon: Adularescence (a blue or white schiller caused by light scattering between microscopic layers of orthoclase and albite).
Hardness & Durability
Origin Region
Prominently Sri Lanka, Madagascar, India, Myanmar, and the Alps in Switzerland
Hardness & Durability
Mohs Hardness: 6.0 to 6.5; Toughness: Poor due to perfect cleavage; brittle and sensitive to pressure and hard knocks.
Care & Maintenance
Clean with warm soapy water and a soft brush; avoid ultrasonic cleaners, steam cleaners, and harsh chemicals; store separately to prevent scratching from harder stones like quartz or topaz.
Rarity & Value
Common to Uncommon; value is dictated by the strength and color of adularescence (blue flash is most valuable), clarity, and size. Typically untreated, though sometimes dyed.
Special Characteristics
Displays adularescence, a 'billowy' light effect that moves across the surface. Can occasionally exhibit chatoyancy (cat's eye) or asterism.
Lore & History
Historically associated with lunar deities and used in Roman and Greek jewelry. Traditionally believed to represent 'new beginnings' and inner growth; often associated with the Crown and Third Eye chakras in crystal healing lore.