mineral

Black Onyx

Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Solid black (often dyed for consistency); Luster: Vitreous to waxy; Texture: Smooth, high-shine polish; Cleavage: None

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

Identified July 19, 2026More mineral →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Solid black (often dyed for consistency); Luster: Vitreous to waxy; Texture: Smooth, high-shine polish; Cleavage: None

Formation & geological history

Formed by the deposition of silica in gas cavities (vesicles) in lava, resulting in the distinctive bands. Natural solid black onyx is rare; most commercial onyx is gray chalcedony that has been dyed black.

Uses & applications

Extensively used in jewelry making for beads, cabochons, and cameos, as well as for decorative carvings and ornamental items.

Geological facts

The name 'onyx' comes from the Greek word for 'claw' or 'fingernail'. In ancient Rome, it was used for seals because it does not stick to wax.

Field identification & locations

Identify by its deep black color, lack of transparency, and weight (heavier than plastic beads). It feels cold to the touch initially compared to glass or acrylic imitations.