mineraloid

Precious Opal

Hydrated silica (SiO2·nH2O)

Hardness: 5.5-6.5; Color: White body with play-of-color (multi-colored flashes); Luster: Subvitreous to waxy; Crystal Structure: Amorphous (non-crystalline spheres); Specific Gravity: 1.9-2.3.

Hardness: 5
Color: White body with play-of-color (multi-colored flashes)
Luster: Subvitreous to waxy

Identified June 2, 2026More mineraloid →

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Physical properties

Hardness: 5.5-6.5; Color: White body with play-of-color (multi-colored flashes); Luster: Subvitreous to waxy; Crystal Structure: Amorphous (non-crystalline spheres); Specific Gravity: 1.9-2.3.

Formation & geological history

Formed from silica-rich water seeping into cracks and cavities in sedimentary or volcanic rock, predominantly during the Cretaceous period. The play-of-color is caused by the diffraction of light through microscopic silica spheres.

Uses & applications

Primarily used in high-end jewelry (rings, pendants, earrings) and as a highly sought-after collector's gemstone.

Geological facts

Opal is the national gemstone of Australia, which produces about 95% of the world's precious opal. Unlike most gemstones, it contains 3% to 21% water by weight.

Field identification & locations

Identify by its characteristic play-of-color (opalescence) which shifts as the stone is turned. It is softer than quartz and can be scratched by a steel blade. Found in arid regions like Coober Pedy, Australia, and parts of Ethiopia.