mineraloid
Opal
Hydrated amorphous silica (SiO2·nH2O)
AI-generated identification · may be incorrectHardness of 5.5-6.5 on the Mohs scale, variable body colors with distinctive play-of-color, subvitreous to greasy luster, and amorphous crystal structure.
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Physical properties
Hardness of 5.5-6.5 on the Mohs scale, variable body colors with distinctive play-of-color, subvitreous to greasy luster, and amorphous crystal structure.
Formation & geological history
Formed from a solution of silica and water filling cracks or voids in sedimentary or volcanic rock over millions of years.
Uses & applications
Extensively used in high-end jewelry, ornamental carvings, and sought after by mineral collectors.
Geological facts
Opal contains up to 20% water trapped within its microscopic silica spheres, which diffract light to create its rainbow effect.
Field identification & locations
Easily identified by its characteristic internal spectral colors and lack of crystalline cleavage; commonly mined in Australia and Ethiopia.
