Opal
Opalline Silica var. Precious Opal · Precious Gemstone
Crystal System
Amorphous (Non-crystalline, typically forms in botryoidal, reniform, or stalactitic masses)
Mineral Group
Mineraloid (Hydrated amorphous silica)
Chemical Formula
SiO2·nH2O
Formation Process
Sedimentary or hydrothermal precipitation from silica-rich groundwater filling fissures or cavities in rocks at low temperatures
About This Crystal
The specimen is a heart-shaped cabochon gemstone featuring a milky-white translucent body tone with vibrant flashes of play-of-color, predominantly displaying bright green, blue, and red pinfires across its surface
Physical Characteristics
Body color is milky white with multicolored play-of-color; white streak; no cleavage; conchoidal to uneven fracture; specific gravity around 2.10 to 2.20; brittle tenacity; displays weak to strong greenish-white fluorescence under UV light
Optical Properties
Isotropic (amorphous, singly refractive); refractive index ranges from 1.370 to 1.470; exhibits prominent play-of-color (diffraction of light caused by ordered microscopic silica spheres)
Hardness & Durability
Origin Region
Australia (Lightning Ridge, Coober Pedy), Ethiopia, Mexico, and the United States; forms in sedimentary or volcanic environments
Hardness & Durability
Mohs hardness of 5.5 to 6.5; poor to fair toughness due to high water content and sensitivity to thermal shock; low wearability for rings unless protected by a secure bezel setting
Care & Maintenance
Clean with warm soapy water using a soft cloth; avoid ultrasonic cleaners, steam, harsh chemicals, sudden temperature changes, and prolonged exposure to extreme dryness or direct sunlight
Rarity & Value
Varies from common to extremely rare; precious opal with bright play-of-color is valuable, with prices depending on body tone, pattern, brilliance, and size; enhancements can include impregnation with oil, wax, or plastic
Special Characteristics
Renowned for its optical phenomenon known as play-of-color, caused by the interference and diffraction of light passing through a regular three-dimensional grid of silica spheres
Lore & History
Historically revered by ancient Romans and Greeks as a symbol of hope and purity; associated with the crown and root chakras in crystal healing traditions, believed to amplify emotions and inspire creativity