mineral

Black Onyx

Silicon Dioxide (SiO2) - Cryptocrystalline Quartz

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs), Color: Solid black or black with white bands, Luster: Vitreous to silky (highly polished in this image), Crystal structure: Trigonal/Hexagonal, Cleavage: None/Conchoidal fracture, Specific Gravity: 2.65-2.67

Hardness: 6

Identified May 24, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica in gas cavities (vesicles) in volcanic lava. It occurs in various geological environments, including metamorphic and sedimentary rocks as nodules or masses.

Uses & applications

Used widely in jewelry (rings, beads, pendants), ornamental carvings, and historical talismans or seals.

Geological facts

While naturally black onyx exists, many commercial specimens are heat-treated and dyed chalcedony to enhance the deep black color. In ancient times, it was believed to provide protection and strength.

Field identification & locations

Identify by its hardness (scratches glass), smooth waxy to vitreous texture, and lack of transparency. Common in Brazil, India, and Madagascar. Collectors look for consistent color and lack of surface pitting.