mineral

Sardonyx

Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7.0 (Mohs scale); Color: Banded reddish-brown, black, and white; Luster: Vitreous to waxy; Crystal structure: Trigonal/Monoclinic; Cleavage: None; Specific gravity: 2.58-2.64

Hardness: 6
Color: Banded reddish-brown, black, and white
Luster: Vitreous to waxy

Identified May 25, 2026More mineral →

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Physical properties

Hardness: 6.5-7.0 (Mohs scale); Color: Banded reddish-brown, black, and white; Luster: Vitreous to waxy; Crystal structure: Trigonal/Monoclinic; Cleavage: None; Specific gravity: 2.58-2.64

Formation & geological history

Formed by the deposition of silica in gas cavities (vesicles) of volcanic rocks. The distinctive bands are created by alternating layers of chalcedony and sard.

Uses & applications

Primarily used in jewelry for cameos, intaglios, beads, and cabochons. Historically used as a protective talisman and in signet rings.

Geological facts

Sardonyx was highly popular in Ancient Rome and Egypt. It is one of the traditional birthstones for August and was believed by Roman soldiers to grant courage and victory in battle.

Field identification & locations

Identify by the distinct, straight parallel bands of brownish-red (sard) and white or black chalcedony. Commonly found in India, Brazil, Germany, and Uruguay. Collectors should look for high contrast in banding.