sedimentary

Grey Chert River Pebble

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs scale; Color: Grey to brownish-grey; Luster: Waxy to dull (earthy when weathered); Crystal structure: Cryptocrystalline; Cleavage: None, exhibits conchoidal fracture; Specific gravity: approx. 2.65.

Hardness: 7 Mohs scale
Color: Grey to brownish-grey
Luster: Waxy to dull (earthy when weathered)

Identified July 20, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed via the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments. This specific specimen has been rounded and smoothed by water transport in a river or coastal environment over thousands of years.

Uses & applications

Primarily used as river rock for landscaping, aggregate in construction, and historically as a tool for sparking or flintknapping.

Geological facts

Chert is extremely durable and chemically stable, which is why it often survives as a pebble long after softer surrounding rocks have eroded away. It is one of the oldest materials used by humans for Paleolithic tools.

Field identification & locations

Identify in the field by its hardness (will scratch glass), smooth texture, and sharp, shell-like edges when broken. It is a very common find in gravel pits, riverbeds, and glacial till throughout North America and Europe.

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