mineral

Black Onyx

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Black with potential faint white bands; Luster: Vitreous when polished; Crystal structure: Trigonal/Microcrystalline; Specific gravity: 2.65-2.677

Hardness: 6
Color: Black with potential faint white bands
Luster: Vitreous when polished

Identified July 7, 2026More mineral →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Black with potential faint white bands; Luster: Vitreous when polished; Crystal structure: Trigonal/Microcrystalline; Specific gravity: 2.65-2.677

Formation & geological history

Formed in the gas cavities of volcanic lava. It occurs when silica-rich minerals are deposited in gas vesicles, typically at low temperatures. Common in various geological environments from volcanic to sedimentary.

Uses & applications

Primarily used in jewelry (rings, beads, pendants), ornamental carvings, and historical cameos. Also popular in gemstone collecting and alternative medicine practices.

Geological facts

The name 'onyx' comes from the Greek word for 'fingernail' or 'claw' because its layering can resemble a fingernail's curve. Black onyx is often naturally a dark chalcedony that has been dyed or heat-treated throughout history to enhance its deep black color.

Field identification & locations

Identify by its hardness (will scratch glass) and lack of transparency. Common locations include Brazil, India, Madagascar, and the USA. Collectors look for consistency in color and the quality of the polished surface.