mineraloid
Opal
Hydrated Silica (SiO2·nH2O)
Hardness: 5.5-6.5; Color: White with iridescent play-of-color; Luster: Subvitreous to pearly; Crystal structure: Amorphous; Fracture: Conchoidal.
- Hardness
- 5
- Color
- White with iridescent play-of-color
- Luster
- Subvitreous to pearly
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Physical properties
Hardness: 5.5-6.5; Color: White with iridescent play-of-color; Luster: Subvitreous to pearly; Crystal structure: Amorphous; Fracture: Conchoidal.
Formation & geological history
Formed from silica-rich water seeping into cracks and cavities in sedimentary or volcanic rock over millions of years, often in arid regions.
Uses & applications
Primarily used as a gemstone in jewelry (rings, pendants, earrings) and as a collector's specimen.
Geological facts
Opals contain between 3% and 21% water. They are the birthstone for October. Most of the world's precious opal is sourced from Australia.
Field identification & locations
Identify by unique 'play-of-color' or opalescence. Found in locations like Coober Pedy (Australia), Ethiopia, and Mexico. Collectors should look for vibrancy of color and lack of cracks (crazing).
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