mineral

Black Onyx

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs scale), Color: Jet black, Luster: Vitreous to waxy, Crystal Structure: Hexagonal/Trigonal, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65-2.67

Hardness: 6

Identified May 11, 2026More mineral →

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Physical properties

Hardness: 6.5-7 (Mohs scale), Color: Jet black, Luster: Vitreous to waxy, Crystal Structure: Hexagonal/Trigonal, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65-2.67

Formation & geological history

Formed in the gas cavities of volcanic lava. Over time, silica-rich water deposits cryptocrystalline quartz layers. Natural solid black onyx is rare; most are dyed chalcedony.

Uses & applications

Primarily used in jewelry for beads, cameos, and carvings. Also used in ornamental architecture and as a protective focus stone in metaphysical practices.

Geological facts

The name comes from the Greek word 'onyx', meaning nail or claw, due to their flesh-colored bands resembling fingernails. Historically used in ancient Egypt and Rome for seals and carvings.

Field identification & locations

Identify by its hardness (cannot be scratched by a steel knife) and its deep, uniform opacity when polished. Commonly found in Brazil, India, Madagascar, and the USA.