mineral

Black Opal (Triplet)

Hydrated Silica (SiO2·nH2O)

Hardness: 5.5-6.5 (Mohs scale), Color: Vivid play-of-color (blue, green), Luster: Vitreous to waxy, Structure: Amorphous (microscopic silica spheres)

Hardness: 5

Identified June 21, 2026More mineral →

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Physical properties

Hardness: 5.5-6.5 (Mohs scale), Color: Vivid play-of-color (blue, green), Luster: Vitreous to waxy, Structure: Amorphous (microscopic silica spheres)

Formation & geological history

Formed from silica-rich water seeping into cracks and cavities in sedimentary or volcanic rocks. Most precious opal is recovered from Australian sedimentary basins (Cretaceous age).

Uses & applications

Primarily used in jewelry as cabochons, pendants, and rings. Triplet opals are manufactured to provide a high-end look at a lower cost.

Geological facts

Opals are non-crystalline minerals called mineraloids. Black opals are the rarest and most valuable; however, triplets consist of a thin slice of opal glued between a dark backing and a clear quartz or glass cap.

Field identification & locations

Identify for multi-layer structure from the side view. High-quality triplets are found in jewelry stores worldwide, with major mining original sources in lightning Ridge, Australia.