mineral

Precious Opal

Hydrated Silica (SiO2·nH2O)

Hardness: 5.5-6.5 (Mohs); Color: White to creamy base with iridescent blue and violet play-of-color; Luster: Vitreous to waxy; Crystal structure: Amorphous; Cleavage: None (conchoidal fracture); Specific gravity: 1.9-2.3

Hardness: 5
Luster: Vitreous to waxy

Identified March 11, 2026More mineral →

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Physical properties

Formation & geological history

Formed from silica-rich water seeping into cracks and cavities within sedimentary host rocks (like sandstone) or volcanic rocks. This specimen appears to be of sedimentary origin, likely from the Cretaceous period (approx. 100 million years ago).

Uses & applications

Primarily used as a gemstone in high-end jewelry (rings, pendants, earrings). Also highly valued by mineral collectors for its unique optical properties.

Geological facts

The 'play-of-color' seen as blue flashes is caused by the diffraction of light as it passes through regularly arranged sub-microscopic spheres of silica. It is the national gemstone of Australia, where the majority of the world's supply is found.

Field identification & locations

Identify in the field by its waxy appearance and 'fire' or flashes of color when rotated in sunlight. Commonly found in Coober Pedy or Lightning Ridge, Australia. Look for veins of glassy material within crumbly sandstone or ironstone matrix.