Mineral

Black Opal

Hydrated Amorphous Silica (SiO2·nH2O)

Hardness: 5.5-6.5 (Mohs); Color: Dark body tone with vibrant play-of-color; Luster: Subvitreous to pearly; Crystal structure: Amorphous; Cleavage: None; Specific gravity: 1.9-2.3

Hardness: 5
Color: Dark body tone with vibrant play-of-color
Luster: Subvitreous to pearly

Identified March 8, 2026More mineral →

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Physical properties

Hardness: 5.5-6.5 (Mohs); Color: Dark body tone with vibrant play-of-color; Luster: Subvitreous to pearly; Crystal structure: Amorphous; Cleavage: None; Specific gravity: 1.9-2.3

Formation & geological history

Formed from silica-rich solution seeping into cracks and voids in sedimentary rock, such as sandstone or ironstone, usually over millions of years. This specimen likely originates from the Cretaceous era in Australia.

Uses & applications

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

Geological facts

It is the rarest and most valuable form of opal. The 'play-of-color' is caused by the diffraction of light as it passes through regularly packed microscopic spheres of silica. It is the official gemstone of Australia.

Field identification & locations

Identify by a dark body tone (N1 to N4) which enhances the brightness of colors. Commonly found in Lightning Ridge, Australia. Collectors look for 'harlequin' or 'pinfire' patterns and a lack of 'potch' (common colorless opal) on the display surface.