gemstone

Black Opal

Hydrated Amorphous Silica (SiO2 "n" H2O)

Hardness: 5.5-6.5 on Mohs scale; Color: Dark body tone (black, dark gray) with internal play-of-color; Luster: Subvitreous to waxy; Structure: Amorphous (non-crystalline); Specific Gravity: 1.9-2.3

Hardness: 5
Luster: Subvitreous to waxy

Identified July 1, 2026More gemstone →

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Physical properties

Hardness: 5.5-6.5 on Mohs scale; Color: Dark body tone (black, dark gray) with internal play-of-color; Luster: Subvitreous to waxy; Structure: Amorphous (non-crystalline); Specific Gravity: 1.9-2.3

Formation & geological history

Formed from silica-rich water seeping into cracks and cavities in sedimentary rocks, then hardening over millions of years. Most common in the Great Artesian Basin of Australia.

Uses & applications

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

Geological facts

Black opals are the most valuable and rare form of opal. The 'play-of-color' is caused by the diffraction of light through microscopic spheres of silica arranged in an orderly pattern.

Field identification & locations

Identify by its dark background color (body tone) paired with vibrant flashes of rainbow colors when rotated in light. Australia, specifically Lightning Ridge, provides over 95% of the world's supply.