mineraloid
Common Opal
SiO2·nH2O (Hydrated Silicon Dioxide)
Hardness: 5.5-6.5 on the Mohs scale, Color: White, brown, and translucent variations, Luster: Vitreous to waxy, Crystal Structure: Amorphous (non-crystalline), Cleavage: None, Specific Gravity: 1.9-2.3
- Hardness
- 5
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Physical properties
Hardness: 5.5-6.5 on the Mohs scale, Color: White, brown, and translucent variations, Luster: Vitreous to waxy, Crystal Structure: Amorphous (non-crystalline), Cleavage: None, Specific Gravity: 1.9-2.3
Formation & geological history
Formed from a solution of silicon dioxide in water, typically deposited at low temperatures in the cracks and cavities of various sedimentary, igneous, and metamorphic rocks.
Uses & applications
Used primarily in lapidary work, jewelry, and as a mineral specimen for collectors.
Geological facts
Unlike precious opal, common opal (sometimes called potch) generally does not display play-of-color, though it can still exhibit attractive translucency and banding.
Field identification & locations
Identified by its conchoidal fracture, lack of crystal faces, and lower specific gravity compared to quartz. Common worldwide, particularly in Australia, Mexico, and the western United States.
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