Moonstone
Orthoclase var. Moonstone (Adularia) · Semi-Precious Gemstone
Crystal System
Monoclinic; commonly occurs in tabular or prismatic crystals, though this specimen is polished into a cabochon.
Mineral Group
Silicates (Tectosilicate); Feldspar group.
Chemical Formula
(K,Na)AlSi3O8
Formation Process
Igneous and Metamorphic; it forms from the intergrowth of two types of feldspar (orthoclase and albite) which separate as the magma cools, creating thin alternating layers.
About This Crystal
An oval-shaped cabochon displaying a milky-white body color with a vitreous to pearly luster. It shows characteristic internal centipede-like fractures and fine lamellae layers which cause light scattering.
Physical Characteristics
Color: White to colorless; Streak: White; Cleavage: Two directions at 90 degrees; Fracture: Conchoidal to uneven; Specific Gravity: 2.56-2.59; Tenacity: Brittle; 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 billowy white or blue glow caused by light diffraction between mineral layers); Doubly refractive.
Hardness & Durability
Origin Region
Prominently sourced from Sri Lanka and India; also found in Madagascar, Myanmar, and the Alps in Europe.
Hardness & Durability
Mohs hardness of 6 to 6.5; Fair toughness but prone to breaking along cleavage planes; Moderate wearability requires protective settings in jewelry.
Care & Maintenance
Avoid ultrasonic and steam cleaners; clean with warm, soapy water and a soft cloth. Store separately from harder gemstones like quartz or diamonds to prevent scratching. Avoid sudden temperature changes.
Rarity & Value
Common to Uncommon; value is dictated by the strength and color of the adularescence (blue is most valuable), clarity, and body color. Natural and generally untreated.
Special Characteristics
Displays adularescence (a 'schiller' effect); may occasionally show chatoyancy or asterism; exhibits internal 'centipede' inclusions which are diagnostic of orthoclase moonstone.
Lore & History
Historically linked to lunar deities and ancient Rome, where it was believed to be formed from frozen moonlight. In traditional crystal healing practices, it is associated with the Crown and Third Eye chakras and is believed to symbolize new beginnings and intuition.