Onyx

Physical Properties

Hardness: 6.5–7 on Mohs scale; Color: typically solid black or black with white bands; Luster: Vitreous to silky; Crystal structure: Trigonal/Monoclinic (Cryptocrystalline); Cleavage: None (Conchoidal fracture)

Formation & Geological History

Formed in the gas cavities of lava (amygdales) or through chemical precipitation in hydrothermal veins. It is a cryptocrystalline variety of quartz that develops at relatively low temperatures.

Uses & Applications

Predominantly used in jewelry (rings, beads, cameos), ornamental carvings, and historical talismans. Occasionally used for small architectural accents.

Geological Facts

In ancient times, onyx was believed to protect the wearer from the 'evil eye' and was favored by Roman soldiers for carving seals of Mars to bring courage in battle.

Field Identification & Locations

Identify by its waxy-to-glassy luster, extreme hardness (it will scratch glass), and its characteristic parallel banding (as opposed to the concentric banding found in agate). Found globally in volcanic regions of Brazil, India, Madagascar, and the USA.

Identified on: 4/26/2026

Mode: Standard