Mineral
Opal
Hydrated Amorphous Silica (SiO2·nH2O)
AI-generated identification · may be incorrectHardness: 5.5-6.5 Mohs. Color: Multi-colored play-of-color on white, black, or fire background. Luster: Vitreous to waxy. Structure: Amorphous (non-crystalline). Cleavage: None. Specific Gravity: 2.09.
- Hardness
- 5
- Luster
- Vitreous to waxy
Identified More mineral →
Explore Opal in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 5.5-6.5 Mohs. Color: Multi-colored play-of-color on white, black, or fire background. Luster: Vitreous to waxy. Structure: Amorphous (non-crystalline). Cleavage: None. Specific Gravity: 2.09.
Formation & geological history
Formed by the deposit of silica-rich water in rock fissures and cavities over millions of years (Cretaceous to recent). Commonly found in sedimentary rocks but can also occur in igneous vesicles.
Uses & applications
Primarily used as a gemstone in jewelry (rings, pendants) and highly valued by mineral collectors for its unique optical properties.
Geological facts
Opals are technically 'mineraloids' rather than minerals because they lack a crystal structure. Precious opal displays 'play-of-color' caused by the diffraction of light through sub-microscopic spheres of silica.
Field identification & locations
Identify by its unique iridescent flash and low density. Commonly found in Coober Pedy (Australia), Ethiopia, and Mexico. Collectors should look for vibrant patterns and body tone.
