mineraloid
Opal
Hydrated amorphous silica (SiO2·nH2O)
AI-generated identification · may be incorrectHardness of 5.5-6.5 on the Mohs scale, waxy to vitreous luster, amorphous crystal structure, and specific gravity around 2.10.
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Physical properties
Hardness of 5.5-6.5 on the Mohs scale, waxy to vitreous luster, amorphous crystal structure, and specific gravity around 2.10.
Formation & geological history
Formed from a solution of silica and water seeping into cracks and voids in sedimentary or volcanic rock over millions of years.
Uses & applications
Used primarily as a precious gemstone in jewelry, decorative carvings, and collector specimens.
Geological facts
Common opal lacks the optical phenomenon known as play-of-color found in precious opals, often displaying a milky or resinous white appearance.
Field identification & locations
Identified by its distinctive conchoidal fracture, lack of crystalline structure, and typical white or yellowish translucent body.
