Moonstone
Feldspar group, Orthoclase var. Moonstone · Semi-Precious Gemstone
Crystal System
Monoclinic system, typically occurring as tabular or prismatic crystals, massive to blocky in metamorphic and igneous rocks.
Mineral Group
Silicates
Chemical Formula
KAlSi3O8 (Potassium aluminum silicate with sodium substitutions forming albite lamellae)
Formation Process
Forms primarily in igneous environments such as granitic pegmatites and felsic intrusive rocks through the cooling and exsolution of alkali feldspar, separating into alternating microscopic layers of orthoclase and albite.
About This Crystal
The specimen is a pear-shaped (cabochon) gemstone set in a decorative bezel ring mounting. It exhibits a translucent to semi-translucent body with a warm brownish-pink or peach-gray base color. A distinct silvery-white sheen and chatoyant linear chatoyancy ripple across the polished surface due to light scattering from micro-lamellar intergrowths.
Physical Characteristics
Color ranges from colorless to white, gray, peach, pink, or brownish with a characteristic pearly to vitreous luster. Streak is white. Shows two directions of perfect to good cleavage at nearly 90 degrees. Fracture is uneven to conchoidal. Specific gravity is approximately 2.56 to 2.58. Tenacity is brittle.
Optical Properties
Biaxial negative with a refractive index ranging between 1.518 and 1.525. Exhibits notable adularescence (a billowy, moonlight-like sheen rolling across the surface caused by the interference of light waves between alternating layers of orthoclase and albite). Doubly refractive.
Hardness & Durability
Origin Region
Notable sources include Sri Lanka, India, Madagascar, Myanmar, Brazil, and the United States. Found in pegmatites, hydrothermal veins, and igneous intrusive rocks.
Hardness & Durability
Mohs hardness of 6 to 6.5. Moderate durability with distinct cleavage planes that make it susceptible to chipping if struck sharply. Requires careful handling when worn in daily-use jewelry like rings.
Care & Maintenance
Clean using warm soapy water and a soft brush; avoid ultrasonic and steam cleaners due to internal fractures and cleavage. Store separately from harder gemstones like quartz or topaz to prevent scratching. Protect from sudden thermal shocks and harsh acids.
Rarity & Value
Common to moderately rare depending on clarity, color saturation, and the strength of adularescence. High-quality specimens with strong blue adularescence or rare body colors command higher prices. Common enhancements are minimal, though some low-grade stones may be dyed or coated.
Special Characteristics
Displays adularescence (schiller effect), which gives the stone its characteristic floating, glowing light source appearance. Inclusions often consist of microscopic centipede-like fracture patterns or tiny lamellar plates.
Lore & History
Historically associated with lunar deities in ancient Roman, Greek, and Indian cultures, where it was believed to be solidified moonbeams. Traditionally viewed as a stone of intuition, emotional balance, and feminine energy, often linked to the crown and third-eye chakras in metaphysical healing lore.