gemstone

Precious Opal

Hydrated amorphous silica, SiO2·nH2O

Mohs hardness of 5.5 to 6.5; displays a play-of-color (iridescence) due to the diffraction of light by microscopic silica spheres; subvitreous to resinous luster; amorphous crystal structure with no cleavage; specific gravity of 1.98 to 2.20.

Identified August 3, 2026More gemstone →

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Physical properties

Formation & geological history

Formed from a solution of silica and water, typically seeping into cracks and voids in sedimentary or volcanic rock over millions of years.

Uses & applications

Used primarily in fine jewelry, as cut and polished gemstones, cabochons, and as a collectible specimen.

Geological facts

Opal contains up to 21% water by weight and can crack or craze if exposed to extreme heat or sudden dryness.

Field identification & locations

Identified easily by its distinctive play-of-color flashing different spectral colors as the viewing angle changes. Found extensively in Australia, Ethiopia, and Mexico.

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Black Opal Ring (Carved Opal)

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