mineral

Black Onyx

Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 Mohs; Color: Black with white banding; Luster: Vitreous to waxy; Crystal Structure: Hexagonal (Trigonal); Cleavage: None/Conchoidal fracture; Specific Gravity: 2.65-2.67

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

Identified June 11, 2026More mineral →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Black with white banding; Luster: Vitreous to waxy; Crystal Structure: Hexagonal (Trigonal); Cleavage: None/Conchoidal fracture; Specific Gravity: 2.65-2.67

Formation & geological history

Formed in the gas cavities (vesicles) of volcanic lava, where silica-rich fluids deposit layers of chalcedony. The black color is often enhanced through ancient drying and dyeing processes or natural carbon inclusions.

Uses & applications

Widely used in jewelry (rings, beads, cameos), ornamental carvings, and historical talismans. Occasionally used in interior decorative accents.

Geological facts

Onyx has been used since antiquity; the Romans used it for seals because wax would not stick to it. Many modern black onyx specimens are actually chalcedony that has been treated to achieve a uniform black color.

Field identification & locations

Identify by its smooth, waxy surface and distinct parallel white banding (unlike Agate, which has curved bands). It is commonly found in Brazil, India, Madagascar, and the USA. Collectors look for high polish and sharp contrast in banding.