mineral

Black Onyx

Cryptocrystalline Quartz (SiO2 with organic/iron impurities)

Hardness: 6.5-7.0 (Mohs scale), Color: Jet black, Luster: Vitreous to waxy, Crystal Structure: Hexagonal (trigonal microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65-2.667

Hardness: 6

Identified June 7, 2026More mineral →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed in the gas cavities (vesicles) of volcanic lava. As silica-rich water percolates into these cavities, it deposits layers of chalcedony. Black onyx is often created through the chemical treatment of gray chalcedony in a sugar-acid solution.

Uses & applications

Extensively used in jewelry (rings, beads, cameos), ornamental carvings, and historical talismans.

Geological facts

In ancient times, onyx was believed to protect against the 'evil eye.' While natural solid black onyx exists, it is extremely rare; most modern black onyx is actually dyed chalcedony, a practice dating back to the Romans.

Field identification & locations

Identify by its smooth, waxy luster and lack of grain. In the field, look for volcanic basalt host rocks. Common locations include Brazil, India, Madagascar, and the US (California/Arizona).

Other mineral specimens

See all

Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Schist

Metamorphic

Epidote

Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)

metamorphic

Nephrite Jade

Nephrite

Mineral/Rock

Banded Gneiss (River Rock/Pebble)

Gneiss (specifically a banded variety often found as a river rock)

Metamorphic Rock

Biotite Schist

Biotite-rich Schist [K(Mg,Fe)3AlSi3O10(F,OH)2]

metamorphic