sedimentary

Chert River Pebble

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Dark grey to brownish-green; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Dark grey to brownish-green
Luster: Waxy to dull

Identified June 18, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Dark grey to brownish-green; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed from the accumulation of silica-rich microfossils (like radiolarians or diatoms) on the ocean floor or through chemical precipitation in groundwater. This specimen has been rounded and smoothed by water transport in a river or coastal environment.

Uses & applications

Historically used for making stone tools (arrowheads/scrapers) due to its sharp edges; currently used as decorative gravel, in construction as aggregate, or as tumbled stones for collectors.

Geological facts

Chert was one of the most important minerals for early humans because its conchoidal fracture creates edges sharper than a steel scalpel. It is chemically identical to flint but usually refers to lighter-colored or non-chalk-associated varieties.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, waxy texture. Look for the curved, shell-like (conchoidal) fractures on the surface. Commonly found in riverbeds and gravel pits.