mineral
Opal
Hydrated Silica (SiO2·nH2O)
AI-generated identification · may be incorrectHardness: 5.5-6.5; Color: Milky white with iridescent play-of-color; Luster: Vitreous to waxy; Structure: Amorphous (non-crystalline); Conchoidal fracture.
- Hardness
- 5
- Color
- Milky white with iridescent play-of-color
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 5.5-6.5; Color: Milky white with iridescent play-of-color; Luster: Vitreous to waxy; Structure: Amorphous (non-crystalline); Conchoidal fracture.
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) and highly valued by mineral collectors for its unique optical properties.
Geological facts
The 'play-of-color' is caused by the diffraction of light through microscopic silica spheres. Unlike most minerals, opal is a mineraloid because it lacks a crystalline structure.
Field identification & locations
Identify in the field by its waxy luster, iridescent flashes (if precious), and presence in volcanic or sedimentary layers. Australia and Ethiopia are major sources.
