mineral
Common Opal
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, and conchoidal fracture. Displays various earthy tones without the spectral play-of-color seen in precious opal.
Identified More mineral →
Explore Common Opal in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness of 5.5 to 6.5 on the Mohs scale, waxy to vitreous luster, and conchoidal fracture. Displays various earthy tones without the spectral play-of-color seen in precious opal.
Formation & geological history
Forms at low temperatures from silica-rich water solutions depositing in the cracks and cavities of sedimentary or volcanic rocks. Geological age varies greatly by deposit.
Uses & applications
Used primarily in lapidary arts, ornamental carvings, and low-cost jewelry or collector displays.
Geological facts
Unlike precious opal, common opal lacks microscopic silica spheres arranged in a regular grid, which prevents the diffraction of light.
Field identification & locations
Identify by its conchoidal fracture, lack of fire/play-of-color, and association with volcanic ash or sedimentary beds. Commonly found in Australia, Mexico, and the western United States.
