mineral

Black Onyx

Silicon dioxide / Chalcedony (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs; Color: Jet black; Luster: Vitreous to silky; Crystal structure: Hexagonal (trigonal) cryptocrystalline; Cleavage: None; Specific Gravity: 2.65-2.67

Hardness: 6
Color: Jet black
Luster: Vitreous to silky

Identified June 10, 2026More mineral →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Jet black; Luster: Vitreous to silky; Crystal structure: Hexagonal (trigonal) cryptocrystalline; Cleavage: None; Specific Gravity: 2.65-2.67

Formation & geological history

Formed through the deposition of silica in gas cavities (vesicles) in lava or igneous rocks. As the silica-rich fluids cool, they crystallize into bands of chalcedony.

Uses & applications

Extensively used in jewelry (rings, beads, pendants), ornamental carvings, and historical intaglios. It is also a popular stone for meditation and gemstone therapy.

Geological facts

Ancient Romans used onyx for carved seals and cameos because the layers could be highlighted; it was often dyed in antiquity to achieve a uniform black color, a practice still common today.

Field identification & locations

Identify in the field by its smooth, waxy texture and conchoidal fracture. Natural black onyx often shows thin white bands; solid black is usually treated. Common in Brazil, India, and Madagascar.