mineral

Black Onyx

Chalcedony (Silicon Dioxide, SiO2)

Hardness: 6.5-7.0 (Mohs scale); Color: Black (sometimes with white banding); Luster: Vitreous to waxy; Crystal Structure: Trigonal (microcrystalline); Specific Gravity: 2.6-2.7

Hardness: 6
Color: Black (sometimes with white banding)
Luster: Vitreous to waxy

Identified July 6, 2026More mineral →

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Physical properties

Hardness: 6.5-7.0 (Mohs scale); Color: Black (sometimes with white banding); Luster: Vitreous to waxy; Crystal Structure: Trigonal (microcrystalline); Specific Gravity: 2.6-2.7

Formation & geological history

Volcanic in origin, formed in the gas cavities (vughs) of lava. It is a cryptocrystalline variety of quartz that develops at relatively low temperatures and pressures over thousands of years as silica-rich water percolates through rock crevices.

Uses & applications

Primarily used in jewelry for beads, cabochons, and cameos. It is also a popular stone for decorative carvings, worry stones, and metaphysical collections.

Geological facts

The name 'onyx' comes from the Greek word for 'fingernail' or 'claw' because of its translucency. While natural black onyx is rare, most commercial black onyx is actually gray chalcedony that has been dyed to achieve a uniform black color, a practice dating back to ancient Roman times.

Field identification & locations

Identify by its smooth, waxy texture and lack of visible crystalline structure. It is frequently found in Brazil, India, Madagascar, and the United States. Collectors look for high polish and consistent saturation of color.