River Agate (Chert/Chalcedony)

Physical Properties

Hardness: 6.5-7 (Mohs). Color: Variegated greens, grays, and whites. Luster: Waxy to vitreous when wet. Crystal structure: Microcrystalline. Cleavage: None (conchoidal fracture).

Formation & Geological History

Formed through the deposition of silica from groundwater in cavities of igneous rocks or sedimentary layers. These specimens were smoothed and rounded over millions of years by river transport and abrasive action.

Uses & Applications

Used primarily for lapidary work, jewelry making (cabochons), and as decorative landscape stone or in rock tumbling.

Geological Facts

River rocks like these are natural 'tumblers'—the moving water and friction against other rocks acts exactly like a mechanical rock tumbler, creating smooth surfaces over centuries.

Field Identification & Locations

Identify in the field by its smoothness, slight translucency at the edges when held to light, and its resistance to scratching with a steel knife. Commonly found in riverbeds and gravel pits.

Identified on: 4/20/2026

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