mineral

Black Onyx

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs. Color: Solid black (often dyed) or black with white bands. Luster: Vitreous to silky. Crystal Structure: Hexagonal (cryptocrystalline). Specific Gravity: 2.65-2.67.

Hardness: 6
Color: Solid black (often dyed) or black with white bands
Luster: Vitreous to silky

Identified July 6, 2026More mineral →

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Physical properties

Hardness: 6.5-7 Mohs. Color: Solid black (often dyed) or black with white bands. Luster: Vitreous to silky. Crystal Structure: Hexagonal (cryptocrystalline). Specific Gravity: 2.65-2.67.

Formation & geological history

Formed as a cryptocrystalline variety of quartz in gas cavities in lava. It is a chalcedony with parallel banding. Natural solid black onyx is rare; most commercial specimens are dyed.

Uses & applications

Used primarily in jewelry (rings, beads, cameos), ornamental carvings, and as a protective stone in metaphysical practices.

Geological facts

The name comes from the Greek word 'onyx', meaning fingernail or claw. In ancient times, much sardonyx was used for seals and intaglio carvings because the wax would not stick to it.

Field identification & locations

Identify by its waxy luster, lack of transparency, and hard surface that can scratch glass. Often confused with black tourmaline or obsidian (which is lighter and has conchoidal fracture).