sedimentary

Chert (Pebble)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs), Color: White, cream, and brown, Luster: Waxy to dull, Crystal Structure: Microcrystalline quartz/Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7

Hardness: 6

Identified July 8, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation from fluids, often in marine environments. This specimen appears water-worn, suggesting a secondary transport process in a river or beach.

Uses & applications

Historically used for making stone tools (flint); currently used in construction aggregate, landscaping, and occasionally as a tumbling stone for hobbyists.

Geological facts

Chert is a very durable rock that often survives long transport in rivers. It is essentially a non-banded form of chalcedony. Some varieties like flint were essential for early human survival for making tools and starting fires.

Field identification & locations

Identify in the field by its hardness (it will scratch glass or steel), waxy appearance on broken surfaces, and typical rounded shapes when found in gravel. Commonly found in riverbeds and limestone outcrops.