mineral

Chalcedony (Agate/Chert)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale. Color: Translucent to opaque, varying from white, grey, brown, to tan. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline (microscopic). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6.

Hardness: 6
Luster: Waxy to vitreous

Identified July 1, 2026More mineral →

Explore Chalcedony (Agate/Chert) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed through the deposition of silica from groundwater in cavities of volcanic or sedimentary rocks. Common in hydrothermal environments and as nodules in limestone or volcanic ash beds.

Uses & applications

Used primarily for lapidary work (jewelry, cabochons), ornamental carvings, and historically for stone tools due to its sharp conchoidal fracture.

Geological facts

Chalcedony is a broad term that includes agate, jasper, and onyx. It was one of the first materials used by early humans to create arrowheads and scrapers because it breaks into predictably sharp edges.

Field identification & locations

Identify in the field by its waxy appearance, smooth conchoidal (shell-like) fracture surfaces, and the fact that it cannot be scratched by a steel knife. Frequently found in riverbeds or desert pavements in volcanic regions.