mineral

Black Onyx

Chalcedony (Silicon Dioxide - SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Deep opaque black; Luster: Vitreous to waxy when polished; Crystal Structure: Trigonal (microcrystalline/cryptocrystalline quartz); Cleavage: None; Specific Gravity: 2.65-2.66.

Hardness: 6
Color: Deep opaque black
Luster: Vitreous to waxy when polished

Identified July 24, 2026More mineral →

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Physical properties

Formation & geological history

Formed at low temperatures through the deposition of silica-rich fluids in gas cavities (vesicles) within volcanic rocks or sedimentary environments.

Uses & applications

Widely used in lapidary art, jewelry (beads, cabochons, rings), ornamental carvings, and metaphysical collections.

Geological facts

Natural solid black onyx is relatively rare; historically, much commercial black onyx has been created by soaking chalcedony or agate in sugar solutions and then treating with acid to carbonize the sugar into a rich black color.

Field identification & locations

Look for a smooth, opaque black appearance with a waxy to glassy polish and high hardness that resists scratching by steel. Common source regions include Brazil, India, Madagascar, Uruguay, and the United States.