mineral

Black Onyx

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs; Color: Jet black (often dyed); Luster: Vitreous when polished; Crystal Structure: Hexagonal (trigonal), microcrystalline; Specific Gravity: 2.65-2.677

Hardness: 6
Color: Jet black (often dyed)
Luster: Vitreous when polished

Identified July 7, 2026More mineral →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Jet black (often dyed); Luster: Vitreous when polished; Crystal Structure: Hexagonal (trigonal), microcrystalline; Specific Gravity: 2.65-2.677

Formation & geological history

Formed in the gas cavities of volcanic rocks through the deposition of silica. Found in various geological ages and secondary deposits like river gravels.

Uses & applications

Used extensively in jewelry for beads, cameos, and intaglios. Historically popular for ornamental carvings and healing stone collections.

Geological facts

Historically, what we call Black Onyx is often natural gray chalcedony that has been dyed black. It is one of the most popular gemstones for signet rings throughout history.

Field identification & locations

Identify by its smooth, glassy surface and high polish. Unlike obsidian, it is unlikely to have tiny bubbles or flow lines. Common locations include Brazil, India, and Madagascar.