Mineral

Opal

Hydrated Amorphous Silica (SiO2·nH2O)

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.

Hardness: 5
Luster: Vitreous to waxy

Identified March 25, 2026More mineral →

Identify your own rocks.

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

App Store Google Play

Physical properties

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.