mineral
Green Opal / Common Opal
Hydrated Silicon Dioxide (SiO2·nH2O)
AI-generated identification · may be incorrectHardness: 5.5-6 on Mohs scale. Color: Apple-green, sea-foam green, and translucent gray-white quartz/opal bands attached to host rock. Luster: Waxy to resinous. Crystal System: Amorphous (non-crystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 1.9-2.3.
- Hardness
- 5
- Luster
- Waxy to resinous
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Physical properties
Hardness: 5.5-6 on Mohs scale. Color: Apple-green, sea-foam green, and translucent gray-white quartz/opal bands attached to host rock. Luster: Waxy to resinous. Crystal System: Amorphous (non-crystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 1.9-2.3.
Formation & geological history
Formed at relatively low temperatures from the deposition of silica-rich fluids in cavities, veins, and fractures of host rocks, often associated with volcanic activity or secondary weathering processes.
Uses & applications
Used for lapidary work, cabochon cutting, decorative carving, and as gemstone or mineral collector display specimens.
Geological facts
Unlike precious opal, green common opal lacks play-of-color ('fire'). Its vibrant green hue is typically caused by micro-inclusions of iron or nickel-bearing silicate minerals such as garnierite, celadonite, or chrysotile.
Field identification & locations
Identified by its distinctive waxy/resinous luster, conchoidal fracturing, light weight relative to quartz, and soft green to translucent body color embedded in matrix rock. Commonly found in Oregon, Washington, Idaho, Australia, Madagascar, and Tanzania.
