mineral
Opal
Hydrated Amorphous Silica (SiO2·nH2O)
AI-generated identification · may be incorrectHardness: 5.5-6.5; Color: White with iridescent play-of-color; Luster: Subvitreous to pearly; Crystal structure: Amorphous; Cleavage: None; Specific Gravity: 1.9-2.3
- Hardness
- 5
- Color
- White with iridescent play-of-color
- Luster
- Subvitreous to pearly
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; Color: White with iridescent play-of-color; Luster: Subvitreous to pearly; Crystal structure: Amorphous; Cleavage: None; Specific Gravity: 1.9-2.3
Formation & geological history
Formed from silica-rich water seeping into fissures and cavities in sedimentary or volcanic rock. Over millions of years, the water evaporates, leaving behind silica deposits that harden into opal.
Uses & applications
Predominantly used as a gemstone in jewelry (rings, pendants, earrings); also highly valued by mineral collectors for unique play-of-color patterns.
Geological facts
Opals are unique because they are non-crystalline 'mineraloids.' The play-of-color is caused by the diffraction of light by small, regularly arranged silica spheres within the stone.
Field identification & locations
Identify by 'fire' or play-of-color under light. Often found in specific regions like lightning ridge in Australia, Ethiopia, or Mexico. It has a greasy or waxy feel compared to quartz.
