mineral

Precious Opal in Matrix

Hydrated Silica (SiO2·nH2O)

Hardness: 5.5-6.5 on Mohs scale; Color: Multi-colored play-of-color (iridescence) within a brown or tan host matrix; Luster: Sub-vitreous to waxy; Crystal structure: Amorphous; Cleavage: None; Specific gravity: 1.9-2.3

Hardness: 5
Luster: Sub-vitreous to waxy

Identified May 19, 2026More mineral →

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Physical properties

Formation & geological history

Formed from silica-rich water seeping into cracks and cavities in sedimentary or volcanic rocks. The 'play-of-color' is caused by the diffraction of light through microscopic silica spheres arranged in a regular pattern. Most commercial deposits date to the Cretaceous period.

Uses & applications

Primarily used in jewelry as cabochons, as well as for lapidary specimens and mineral collecting.

Geological facts

Opal contains between 3% and 21% water by weight. It is the national gemstone of Australia, which produces roughly 95% of the world's precious opal supply.

Field identification & locations

Identify in the field by looking for flashes of spectral colors within a duller host rock when rotated under a light source. Commonly found in arid regions like Coober Pedy (Australia), Ethiopia, and Mexico. Collectors should look for 'matrix opal' where the precious opal is naturally embedded in the stone.