mineral

Chalcedony (Common Agate)

Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 Mohs; Color: Tan, orange-brown, translucent; Luster: Waxy to vitreous; Crystal Structure: Trigonal/Monoclinic (Microscopic); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.58-2.64

Hardness: 6
Color: Tan, orange-brown, translucent
Luster: Waxy to vitreous

Identified July 20, 2026More mineral →

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Physical properties

Formation & geological history

Formed via the deposition of silica from groundwater in cavities of volcanic and sedimentary rocks. This specimen likely weathered out of a host rock and was rounded by alluvial or marine action.

Uses & applications

Used for carvings, cabochon jewelry, beads, and as decorative gravel. Industrially used for mortars and pestles due to its hardness and chemical resistance.

Geological facts

Chalcedony is composed of microscopic intergrowths of quartz and moganite. When it exhibits banding, it is specifically called agate. It has been used since the Bronze Age for making cylinder seals and jewelry.

Field identification & locations

Identified in the field by its waxy luster, conchoidal (shell-like) fracture, and inability to be scratched by a steel knife. Commonly found in riverbeds, beaches, and volcanic regions.

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