Opal
Mineraloid Opal var. Precious Opal · Precious Gemstone
Crystal System
Amorphous (Non-crystalline, lacks a defined crystal lattice)
Mineral Group
Silicate mineraloid
Chemical Formula
SiO2·nH2O
Formation Process
Sedimentary or weathering processes involving silica-rich water seeping into cracks and voids in rock layers, precipitating microscopic silica spheres over millions of years.
About This Crystal
An oval-cut gemstone set in a gold ring, displaying a milky-white body tone with vivid flashes of spectral color (play-of-color) primarily in cyan, green, and blue hues. The gem is semi-translucent with a vitreous to resinous luster.
Physical Characteristics
White to milky body color with multi-colored play-of-color; white streak; no cleavage; conchoidal to uneven fracture; specific gravity around 2.10; brittle tenacity; typically inert to moderate greenish fluorescence under UV light.
Optical Properties
Refractive index ranges from 1.370 to 1.470; exhibits strong play-of-color (opalescence) caused by the diffraction of light through an orderly grid of microscopic silica spheres. Isotropic due to amorphous structure.
Hardness & Durability
Origin Region
Australia (Coober Pedy, Lightning Ridge), Mexico, Ethiopia, and the United States (Nevada)
Hardness & Durability
Mohs hardness of 5.5 to 6.5; poor toughness and high sensitivity to thermal shock, sudden temperature changes, and dehydration. Requires protective settings for jewelry use.
Care & Maintenance
Clean with warm, soapy water only; avoid ultrasonic and steam cleaners, harsh chemicals, cosmetics, and sudden temperature shifts. Store away from extreme dryness or prolonged direct sunlight to prevent crazing.
Rarity & Value
Varies from common to rare; precious opals with vivid play-of-color command high prices depending on body tone, pattern, brightness, and origin. Common treatments include impregnation with oil, wax, or plastic, and smoke treatment for black opals.
Special Characteristics
Famous for its vibrant play-of-color (diffraction of white light into spectral colors due to regular internal packing of sub-microscopic silica spheres).
Lore & History
Historically revered by ancient Romans and Greeks as a symbol of hope and purity, though some Victorian superstitions associated it with bad luck. In modern crystal healing, opal is associated with the root and sacral chakras, symbolizing emotional expression, transformation, and creativity.