Sardonyx Cameo

Physical Properties

Hardness: 6.5-7 (Mohs); Color: Banded layers of brownish-red (sard) and white (onyx); Luster: Vitreous to waxy; Structure: Hexagonal (trigonal); Cleavage: None; Specific Gravity: 2.58–2.64.

Formation & Geological History

Formed through the deposition of silica in gas cavities (vesicles) in volcanic rock. The distinct bands of color come from varying amounts of iron and other impurities during the hydrothermal crystallization process.

Uses & Applications

Primary use is in jewelry and lapidary arts, specifically for carvings such as cameos and intaglios where the layered colors can be utilized for artistic depth.

Geological Facts

Cameos have been carved since ancient Roman times. Sardonyx was highly valued by Roman soldiers who wore rings carved with Mars to bring bravery in battle. It is one of the traditional birthstones for August.

Field Identification & Locations

Identify by distinct, straight, parallel bands of red-brown and white. Genuine stone will feel cold to the touch and cannot be scratched by a steel needle, unlike plastic imitations. Common locations include Brazil, India, and Uruguay.

Identified on: 4/25/2026

Mode: Standard