mineral

Sardonyx Agate Sphere

Cryptocrystalline Quartz (SiO2) with iron oxide inclusions

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs scale), Color: Banded layers of brownish-orange, black, and white. Luster: Vitreous to waxy. Crystal Structure: Hexagonal (microcrystalline). Cleavage: None (conchoidal fracture).

Hardness: 6
Color: Banded layers of brownish-orange, black, and white
Luster: Vitreous to waxy

Identified May 12, 2026More mineral →

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Physical properties

Formation & geological history

Formed in silica-rich volcanic lava cavities where mineralized water deposits layers of chalcedony over thousands of years. The distinctive bands are caused by varying mineral concentrations in the groundwater.

Uses & applications

Used primarily in jewelry, ornamental carvings, lapidary art, and as a collector's specimen. Historically used for making signet rings and cameos.

Geological facts

Sardonyx was highly prized by the ancient Romans who believed it could protect them from evil. It was often engraved with the figure of Mars to encourage bravery in battle.

Field identification & locations

Identified by its distinctive parallel, high-contrast banding and hardness. To identify in the field, look for nodules with a waxy exterior and internal banding when broken; often found in river beds or areas with volcanic history.