sedimentary

Chert (Pebble)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Grayish-brown to dark gray; Luster: Waxy to dull; Fracture: Conchoidal; Structure: Microcrystalline/Cryptocrystalline quartz

Hardness: 6
Color: Grayish-brown to dark gray
Luster: Waxy to dull

Identified July 26, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Grayish-brown to dark gray; Luster: Waxy to dull; Fracture: Conchoidal; Structure: Microcrystalline/Cryptocrystalline quartz

Formation & geological history

Formed through the accumulation and precipitation of silica-rich biogenic ooze or chemical replacement in marine sedimentary environments. Subsequently rounded and smoothed by water erosion.

Uses & applications

Historically used for flintknapping to make tools and weapons; currently used for river rock gravel, tumbling, and general geological study.

Geological facts

Chert is a hard, fine-grained sedimentary rock composed of microcrystals of quartz. Smooth, water-worn chert pebbles like this are frequently found in riverbeds and along beaches.

Field identification & locations

Identify in the field by its hardness (scratches glass), smooth waxy feel, and characteristic curved conchoidal fracture edges. Widely found in gravel bars, stream beds, and ocean coastlines globally.