White Opal
Hydrated Silica var. Precious White Opal · Precious Gemstone
Crystal System
Amorphous (Non-crystalline) aggregate of silica spheres; often occurs in massive or vein-filling habits.
Mineral Group
Silicates (Tectosilicate class, though technically a mineraloid)
Chemical Formula
SiO2·nH2O
Formation Process
Sedimentary precipitation; silica-rich water seeps into rock cavities and evaporates, leaving behind hardened silica spheres.
About This Crystal
White to creamy body color with a translucent to opaque appearance. Surfaces often show 'play-of-color' (iridescence) and a sub-vitreous to waxy luster.
Physical Characteristics
White body color, white streak, no cleavage, conchoidal fracture, specific gravity 1.9–2.3, often inert but can fluoresce white-green under UV.
Optical Properties
Isotropic (Singly Refractive) with an RI of 1.37–1.47; characterized by opalescence and play-of-color due to light diffraction between silica spheres.
Hardness & Durability
Origin Region
Mainly South Australia (Coober Pedy, Andamooka) and Ethiopia (Welo region).
Hardness & Durability
Mohs hardness 5.5–6.5; low toughness (brittle), sensitive to thermal shock and dehydration which causes 'crazing' (cracking).
Care & Maintenance
Avoid ultrasonic cleaners and harsh chemicals; clean with mild soapy water and a soft cloth; store in a cool, slightly humid environment to prevent drying.
Rarity & Value
Relatively common compared to Black Opal, but high-quality patterns increase value. Frequently treated with resins or dyes to hide cracks or enhance color.
Special Characteristics
Play-of-color (diffraction of light), opalescence, and high water content (usually 3% to 21% by weight).
Lore & History
Traditionally associated with purity, hope, and emotional intensification. In ancient Rome, it was a symbol of love and good fortune; in later centuries, it was mistakenly associated with bad luck.