mineraloid
Green Opal
Hydrated amorphous silica (SiO2·nH2O) with inclusions
Hardness: 5.5-6.5; Color: Olive, pistachio, or lime green; Luster: Vitreous to waxy; Structure: Amorphous; Fracture: Conchoidal; Specific Gravity: 1.9-2.3
- Hardness
- 5
- Color
- Olive, pistachio, or lime green
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 5.5-6.5; Color: Olive, pistachio, or lime green; Luster: Vitreous to waxy; Structure: Amorphous; Fracture: Conchoidal; Specific Gravity: 1.9-2.3
Formation & geological history
Formed at low temperatures from silica-rich waters in fractures of various rock types, often associated with volcanic environments or serpentine deposits. The green color usually comes from inclusions of nontronite or iron minerals.
Uses & applications
Primarily used for lapidary work, jewelry (cabochons), and as decorative display specimens or metaphysical stones.
Geological facts
Unlike 'precious opal,' common green opal does not show a play-of-color (opalescence) but is prized for its vibrant, uniform earthy hues.
Field identification & locations
Identify by its waxy luster and smooth, shell-like (conchoidal) fracture surfaces. Commonly found in Madagascar, Tanzania, and Serbia.
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