mineral

Black Opal

Hydrated Silica (SiO2·nH2O)

Hardness: 5.5-6.5 (Mohs); Color: Dark body tone (black, dark gray, or dark green) with play-of-color; Luster: Subvitreous to waxy; Crystal structure: Amorphous; Cleavage: None; Specific gravity: 1.9-2.3

Hardness: 5
Luster: Subvitreous to waxy

Identified June 19, 2026More mineral →

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Physical properties

Formation & geological history

Formed in the cracks and cavities of sedimentary rocks through the evaporation of silica-rich water. Most black opals were formed during the Cretaceous period, roughly 100 million years ago.

Uses & applications

Primarily used as a gemstone in high-end jewelry (rings, pendants) and highly valued by mineral collectors.

Geological facts

Black opals are the rarest and most valuable type of opal. Lightning Ridge in New South Wales, Australia, is the world's primary source for high-quality black opal.

Field identification & locations

Identify by looking for a dark body background that makes the 'play-of-color' (fire) appear more vibrant. Unlike other stones, the colors shift when the stone is viewed from different angles. Found mostly in Australia.