mineral

Opal

Hydrated Amorphous Silica (SiO2·nH2O)

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

Hardness: 5
Color: White with iridescent play-of-color
Luster: Subvitreous to pearly

Identified May 30, 2026More mineral →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

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.