sedimentary

Chert (Flint nodule)

Microcrystalline / Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7.0 on the Mohs scale; Color: Gray, tan, whitish weathering rind with smooth waxy inner fractures; Luster: Dull to waxy/vitreous; Cleavage: None (conchoidal fracture); Specific gravity: ~2.5 - 2.8

Hardness: 7
Luster: Dull to waxy/vitreous

Identified November 15, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed via biochemical or chemical precipitation of silica in marine environments, often replacing carbonate minerals within limestone or chalk formations. Many nodules date from the Paleozoic through Cretaceous periods.

Uses & applications

Historically used for stone tools, flintknapping arrowheads, and spark-striking fire starters. Modern uses include road aggregates, grinding media, and decorative rocks.

Geological facts

Flint was crucial to the Stone Age revolution, enabling the creation of exceptionally sharp blades and the ignition of fire via percussion with iron pyrite or steel.

Field identification & locations

Look for a smooth, porcelain-like or waxy conchoidal fracture surface surrounded by a rougher, chalky weathering cortex. Common in river beds, glacial drift, and chalk/limestone cliffs.