sedimentary

Flint or chert pebble

Microcrystalline quartz (SiO₂), commonly called chert or flint

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; dark gray to black, with a dull-to-waxy luster and white/cream patches likely from weathering or included silica. It is dense, non-cleavable, cryptocrystalline, and typically breaks with conchoidal fracture.

Identified August 30, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces or fills pores in limestone and other sediment, commonly during the Paleozoic–Cenozoic eras; the exact age cannot be determined visually. Surface rounding indicates transport as a pebble.

Uses & applications

Used historically for cutting tools, fire-starting, and arrowheads; attractive pieces may be collected, but this small specimen has little commercial value.

Geological facts

Flint is technically a dark variety of chert, often associated with chalk or limestone. Freshly fractured surfaces are sharper and more glasslike than the weathered exterior.

Field identification & locations

Look for extreme hardness, a smooth waxy texture, conchoidal edges, and inability to scratch it with a steel knife; it should scratch glass. Common in gravel beds, stream deposits, and limestone regions worldwide.