sedimentary

Chert Pebble

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale), Color: dull gray to blue-gray, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.6-2.7.

Identified July 15, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: dull gray to blue-gray, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.6-2.7.

Formation & geological history

Formed primarily through the precipitation of silica from seawater or ground fluids, often replacing organic material or filling voids in limestone. This specimen shows signs of fluvial or glacial transport, rounding its edges into a pebble.

Uses & applications

Historically used for stone tools (flintknapping); currently used in construction aggregate, road base, and as decorative river rock in landscaping.

Geological facts

Chert is so hard it can scratch steel and produce sparks when struck against iron. It is one of the most durable rocks found in riverbeds and glacial tills.

Field identification & locations

Identify in the field by its smooth, waxy texture and curved, glass-like (conchoidal) fractures. Commonly found in riverbeds, lake shores, and gravel pits across North America and Europe.