mineral
Common Opal in Matrix
Hydrated amorphous silica (SiO2·nH2O)
AI-generated identification · may be incorrectHardness of 5.5 to 6.5 on the Mohs scale, waxy to vitreous luster, amorphous crystal structure, and conchoidal fracture. Colors vary widely from brown and tan host rock to white and yellow opal infill.
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Physical properties
Hardness of 5.5 to 6.5 on the Mohs scale, waxy to vitreous luster, amorphous crystal structure, and conchoidal fracture. Colors vary widely from brown and tan host rock to white and yellow opal infill.
Formation & geological history
Formed at low temperatures from the deposition of silica-rich aqueous solutions in rock cavities, faults, and sedimentary strata.
Uses & applications
Used primarily as a lapidary material, gemstone carving, and as a collectible geological specimen.
Geological facts
Unlike precious opal, common opal typically lacks the internal play-of-color diffraction. It is found worldwide wherever silica-bearing hydrothermal waters interact with host rock.
Field identification & locations
Identify by its waxy luster filling cavities within brownish host rock and lack of cleavage. Common in volcanic regions and sedimentary deposits globally.
