Moonstone
Feldspar group, Orthoclase var. Moonstone · Semi-Precious Gemstone
Crystal System
Monoclinic; typically found as massive to platy aggregates or prismatic crystals.
Mineral Group
Silicates (Tectosilicates)
Chemical Formula
(K,Na)AlSi3O8
Formation Process
Igneous and metamorphic; forms as cooling magma crystallizes into pegmatites or through high-temperature metamorphic processes where potassium and sodium feldspars intergrow.
About This Crystal
The specimen is a polished oval cabochon of a pale whitish-greenish to translucent body color, displaying a soft vitreous to pearly luster and a characteristic glowing adularescent sheen.
Physical Characteristics
Body color is milky white to soft green with a white streak. It exhibits two directions of perfect to good cleavage at nearly right angles, an uneven to conchoidal fracture, and a specific gravity around 2.56-2.58. Tenacity is brittle.
Optical Properties
Biaxial negative with a refractive index ranging between 1.518 and 1.526. The defining optical phenomenon is adularescence, a billowy, moon-like light sheen caused by the scattering of light from microscopic alternating layers of orthoclase and albite.
Hardness & Durability
Origin Region
Sri Lanka, India, Madagascar, Myanmar, Brazil, and the United States; typically forms in igneous pegmatites and metamorphic rocks.
Hardness & Durability
Mohs hardness of 6 to 6.5. It has fair to good durability, but perfection cleavage makes it somewhat susceptible to chipping under sharp impacts. Suitable for rings with protective settings and pendants.
Care & Maintenance
Clean with warm soapy water and a soft brush; avoid ultrasonic cleaners, harsh chemicals, and sudden thermal shock. Store separately from harder gemstones to prevent scratching.
Rarity & Value
Uncommon to Rare depending on the intensity and color of the adularescence (blue adularescence being the most prized). Prices range from affordable to moderate for fine-grade cabochons. Common treatments include coating or dyeing in lower-grade specimens.
Special Characteristics
Adularescence (schiller effect), resulting from light diffraction within microscopic lamellar intergrowths of two different feldspars.
Lore & History
Historically associated with lunar deities in various ancient cultures, including Roman and Hindu lore. In modern crystal healing, it is traditionally connected with intuition, inner growth, balance, and the third eye and crown chakras (note: these are traditional beliefs and not scientific claims).