sedimentary

Flint or chert nodule

Microcrystalline quartz (SiO₂), commonly chalcedony with possible minor impurities

AI-generated identification · may be incorrect

Typically Mohs hardness 6.5–7, brown to gray coloration, waxy to dull luster, very fine-grained cryptocrystalline structure, and conchoidal fracture; no visible cleavage. The pale patches may be weathering or incorporated lighter material.

Identified September 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms mainly by replacement of limestone or accumulation and cementation of siliceous sediment, often during the Cretaceous or other Phanerozoic periods. Nodules commonly develop within marine carbonate rocks.

Uses & applications

Used historically for flint tools and fire-starting, and occasionally as decorative or lapidary material. Ordinary specimens have little commercial value.

Geological facts

Fresh fractures are commonly sharp-edged and glass-like, producing a distinctive conchoidal surface. Flint is generally darker and more uniform than many varieties of chert, but the terms overlap.

Field identification & locations

Look for hardness sufficient to scratch glass, a smooth waxy fracture, and resistance to dilute acid; surrounding limestone may fizz even though the chert does not. Common in chalk and limestone regions worldwide, including England, France, Texas, Kansas, and the Great Lakes area.