mineral

Black Onyx (Tumbled)

Silicon Dioxide (SiO2)

Hardness: 6.5-7.0 (Mohs scale), Color: Jet black, Luster: Vitreous to waxy, Crystal Structure: Hexagonal (trigonal) cryptocrystalline, Cleavage: None, Specific Gravity: 2.65-2.67

Hardness: 6

Identified July 6, 2026More mineral →

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Physical properties

Hardness: 6.5-7.0 (Mohs scale), Color: Jet black, Luster: Vitreous to waxy, Crystal Structure: Hexagonal (trigonal) cryptocrystalline, Cleavage: None, Specific Gravity: 2.65-2.67

Formation & geological history

Formed through the deposition of silica in gas cavities (vesicles) in lava. Most solid black onyx sold today is naturally occurring gray chalcedony that has been dyed to achieve a uniform black color, a practice dating back to ancient Roman times.

Uses & applications

Extensively used in jewelry (beads, cabochons, rings), ornamental carvings, intaglios, and as a spiritual stone in metaphysical practices.

Geological facts

The name comes from the Greek word 'onux', meaning claw or fingernail. According to legend, Cupid cut the fingernails of Venus and her parings fell to earth, turning into onyx. While banded onyx is natural, solid black onyx is rare in nature.

Field identification & locations

Identify by its waxy luster, lack of visible grain, and hardness (it should not be scratched by a steel knife). Commonly found in Brazil, India, Madagascar, and the USA.