Moonstone
Orthoclase var. Moonstone (Adularia) · Semi-Precious Gemstone
Crystal System
Monoclinic; typically found in massive, tumbled, or tabular habits with characteristic exsolution lamellae.
Mineral Group
Silicates (Tectosilicate), Feldspar Group, Alkali Feldspar Subgroup
Chemical Formula
(K,Na)AlSi3O8 (Potassium Aluminum Silicate with trace Sodium)
Formation Process
Forms primarily in hydrothermal veins and pegmatites. The characteristic optical effect occurs as the mineral cools, causing the orthoclase and albite to separate into alternating microscopic layers.
About This Crystal
A translucent to semi-transparent tumbled stone with a creamy to tan body color. It features internal banding and a characteristic pearly to vitreous luster. When held to light, it exhibits a 'shiller' or adularescence effect across its internal structural planes.
Physical Characteristics
Color: Colorless, white, peach, or grey. Streak: White. Cleavage: Perfect in two directions at nearly 90 degrees. Fracture: Uneven to conchoidal. Specific Gravity: 2.56-2.59. Tenacity: Brittle. Fluorescence: Weak bluish or orange under UV.
Optical Properties
Refractive Index: 1.518–1.526. Birefringence: 0.005–0.008. Characterized by adularescence (a ghostly blue or white sheen caused by light scattering off internal lamellae layers). Doubly refractive.
Hardness & Durability
Origin Region
Major sources include Sri Lanka (classic blue sheen), Madagascar, India (rainbow/multi-color varieties), Myanmar, and Tanzania.
Hardness & Durability
Mohs Hardness: 6.0 - 6.5. Toughness: Poor due to perfect cleavage. Wearability is moderate; it is prone to scratching and can chip if struck along cleavage planes.
Care & Maintenance
Clean with warm soapy water and a soft brush. Avoid ultrasonic and steam cleaners. Store separately from harder stones like quartz or sapphire to prevent scratching. Sensitive to sudden temperature changes.
Rarity & Value
Common to Uncommon. Value is dictated by the strength and color of the adularescence (blue is most prized), transparency, and lack of visible internal fractures. Untreated is standard.
Special Characteristics
Features adularescence, a light-scattering phenomenon. Some specimens may show chatoyancy (cat's eye) or asterism (star effect) depending on inclusions and cutting orientation.
Lore & History
Historically used in Roman and Greek jewelry, associated with lunar deities. Legend says moonstone is formed from frozen moonbeams. Symbolically linked to intuition, feminine energy, and new beginnings in traditional cultural lore.