mineral

Opal

Hydrated amorphous silica (SiO2·nH2O)

AI-generated identification · may be incorrect

Mohs hardness of 5.5-6.5; displays vitreous to sub-resinous luster and a sub-conchoidal fracture. Often exhibits a play-of-color phenomenon due to internal microscopic silica spheres.

Identified October 20, 2026More mineral →

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Physical properties

Mohs hardness of 5.5-6.5; displays vitreous to sub-resinous luster and a sub-conchoidal fracture. Often exhibits a play-of-color phenomenon due to internal microscopic silica spheres.

Formation & geological history

Forms from low-temperature precipitation of silica-rich groundwater in sedimentary or volcanic rock cavities. Typically develops over thousands to millions of years in arid environments.

Uses & applications

Extensively used in fine jewelry, including rings, pendants, and collector display specimens. High water content makes it sensitive to heat and sudden pressure changes.

Geological facts

Australia produces over 90% of the world's precious opal supply. Ancient Romans considered opal the most precious and powerful of all gemstones.

Field identification & locations

Identify by its characteristic play-of-color, lower specific gravity compared to quartz, and amorphous structure without true crystal faces. Commonly sourced from Australia, Ethiopia, and Mexico.