mineraloid

Black Opal

Hydrated silica (SiO2·nH2O)

Hardness: 5.5-6.5 Mohs; Color: Dark body tone (N1 to N4) with play-of-color; Luster: Vitreous to waxy; Crystal structure: Amorphous; SG: 1.9-2.3

Hardness: 5
Color: Dark body tone (N1 to N4) with play-of-color
Luster: Vitreous to waxy

Identified April 14, 2026More mineraloid →

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Physical properties

Hardness: 5.5-6.5 Mohs; Color: Dark body tone (N1 to N4) with play-of-color; Luster: Vitreous to waxy; Crystal structure: Amorphous; SG: 1.9-2.3

Formation & geological history

Formed from silica-rich water seeping into cracks and cavities in sedimentary or volcanic rock, often in cretaceous layers. As water evaporates, silica spheres settle to form opal.

Uses & applications

Primarily used as a high-value gemstone in fine jewelry, including rings, pendants, and as investment-grade collector specimens.

Geological facts

Black opal is the rarest and most valuable variety of opal. Its dark body color acts as a backdrop that makes the 'play-of-color' much more intense than in white or crystal opals.

Field identification & locations

Identify by a dark base color (black, dark grey, or dark green) when viewed from the top. Major source is Lightning Ridge, Australia. Watch for 'doublets' or 'triplets' where a thin slice is glued to a backing.