mineral

Tumbled Onyx / Black Chalcedony

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale. Color: Deep black, often with subtle banding or dark grayish tones. Luster: Vitreous to waxy when polished. Crystal Structure: Microcrystalline/Cryptocrystalline trigonal aggregate. Cleavage: None, exhibits conchoidal fracture.

Hardness: 6
Color: Deep black, often with subtle banding or dark grayish tones
Luster: Vitreous to waxy when polished

Identified July 26, 2026More mineral →

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Physical properties

Formation & geological history

Formed at low temperatures through the deposition of silica-rich solutions in gas cavities within volcanic rocks (basalts or andesites) or sedimentary layers.

Uses & applications

Widely used in lapidary arts, jewelry, carved ornaments, beads, decorative stones, and metaphysical practices.

Geological facts

Black onyx has been used in jewelry and carving since antiquity. In ancient Rome, it was highly prized for carving cameos because the layers allowed artists to create white figures on dark backgrounds.

Field identification & locations

Identified by its smooth tumbled surface, conchoidal fracture marks under high light, deep black color, and high hardness (scratches glass). Commonly found in Brazil, India, Madagascar, and the United States.

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