Precious Opal
Opal (hydrated silica mineraloid) · Precious Gemstone / Mineral Specimen
Crystal System
Amorphous (Non-crystalline); commonly found in massive, botryoidal, or vein-filling habits within host rock.
Mineral Group
Silicates (Tectosilicate / Mineraloid)
Chemical Formula
SiO2·nH2O
Formation Process
Sedimentary/Hydrothermal. Forms from silica-rich water seeping into cracks and voids; as water evaporates, silica spheres deposit in ordered structures.
About This Crystal
This specimen shows internal play-of-color known as opalescence. It features a translucent body with iridescent flashes of green, pink, and violet, nestled in a dark, potentially basaltic or carbonaceous matrix.
Physical Characteristics
Color: Colorless to white base with play-of-color; Streak: White; Cleavage: None; Fracture: Conchoidal to uneven; Specific Gravity: 1.9-2.3; Fluorescence: Can be inert to white/green under UV.
Optical Properties
Isotropic (Singly refractive); Refractive Index: 1.37-1.47; Dispersion: None; Phenomenon: Play-of-color caused by diffraction of light through silica spheres.
Hardness & Durability
Origin Region
Notably Australia (Coober Pedy, Lightning Ridge), Ethiopia (Welo), and Mexico. Often found in sedimentary or volcanic host rocks.
Hardness & Durability
Mohs hardness: 5.5-6.5; Toughness: Very brittle/Poor; Sensitivity: Susceptible to temperature shock and dehydration (crazing).
Care & Maintenance
Avoid ultrasonic cleaners and steam. Clean with warm soapy water. Store in a cool place, occasionally away from bright lights to prevent drying. Avoid harsh chemicals.
Rarity & Value
Precious opal is rare. Value is determined by 'fire' intensity, color variety, pattern, and matrix contrast. Treatments like sugar-acid carbonization or smoke treatment are possible in matrix specimens.
Special Characteristics
Play-of-color (iridescence) and potentially a 'matrix opal' configuration where the opal resides directly within the host stone voids.
Lore & History
Historically associated with luck and purity in ancient Rome. In modern lore, it is believed to enhance creativity and emotional expression; associated with the Crown Chakra.