sedimentary

Chert (River Pebble)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: typically dark brown, grey, or black; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 7 on Mohs scale
Color: typically dark brown, grey, or black
Luster: waxy to dull

Identified June 2, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: typically dark brown, grey, or black; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation from sea water. This specific specimen has been smoothed by water transport in a river or coastal environment.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp fracture; currently used in construction aggregate, landscaping, and sometimes as a polishing medium.

Geological facts

Chert is extremely durable and chemically stable, allowing it to survive long-distance transport in rivers. It has been used by humans for hundreds of thousands of years to create fire by striking it against steel or pyrite.

Field identification & locations

Identify in the field by its hardness (will scratch glass), smooth waxy texture when wet, and its characteristic curved (conchoidal) shell-like breaks. It is ubiquitous in gravel bars and riverbeds worldwide.