Black Opal

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.

Identified on: 4/14/2026

Mode: Standard