mineral

Chalcedony (Agate / Chert)

Silicon Dioxide (SiO2)

Hardness: 6.5 - 7 on Mohs scale. Color: Translucent yellowish-tan to honey-brown with white rind and weathered exterior. Luster: Waxy to vitreous (glassy). Fracture: Conchoidal. Crystal system: Microcrystalline trigonal.

Hardness: 6
Luster: Waxy to vitreous (glassy)

Identified July 28, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica from water solutions at low temperatures in cavities, fractures, and pore spaces within volcanic host rocks or sedimentary environments.

Uses & applications

Used widely in lapidary arts, jewelry, cabochon carving, decorative stone displays, and as a popular collectible among rockhounds.

Geological facts

Chalcedony is a cryptocrystalline form of silica, composed of micro-intergrowths of quartz and moganite. The translucent body paired with a distinct weathering cortex/rind is a classic hallmark of river-worn or desert-weathered agates and nodules.

Field identification & locations

Look for a smooth waxy texture, curved conchoidal fractures, translucency when backlit, and a distinct outer weathering crust. Commonly found along gravel bars, river beds, volcanic gravel deposits, and alluvial beaches worldwide.