mineral

Black Onyx (Tumbled)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Jet black (often dyed for consistency); Luster: Vitreous to waxy; Crystal Structure: Hexagonal (trigonal microcrystalline); Cleavage: None; Specific Gravity: 2.65-2.66

Hardness: 6
Color: Jet black (often dyed for consistency)
Luster: Vitreous to waxy

Identified March 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 as a cryptocrystalline variety of quartz (chalcedony) in gas cavities of volcanic rocks or within veins through low-temperature hydrothermal processes. It can range from ancient Precambrian to more recent Cenozoic formations.

Uses & applications

Used widely in jewelry (rings, beads, pendants), ornamental carvings, and historical intaglios. In metaphysical circles, it is used as a 'grounding' stone.

Geological facts

Natural onyx is usually banded with white and black layers; most solid jet-black onyx sold today is actually gray chalcedony that has been dyed black using a traditional sugar-sulfuric acid treatment dating back to Roman times.

Field identification & locations

Identify in the field by its conchoidal fracture, lack of visible crystals, and hardness (cannot be scratched by a steel knife). Commonly found in Brazil, India, Madagascar, and the US (California and Oregon).