sedimentary

Dark gray flint or chert fragment

Microcrystalline quartz (SiO₂), commonly called chert or flint

AI-generated identification · may be incorrect

Typically Mohs hardness 6.5–7, dull to waxy luster, gray to black color, very fine-grained cryptocrystalline structure, and no visible cleavage. The angular fragment appears consistent with conchoidal fracturing, though the image cannot confirm the diagnosis.

Identified August 31, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces or fills pores in limestone and other sediments, often during diagenesis; many examples are Paleozoic to Cenozoic. Common in sedimentary basins, limestone formations, and gravel deposits worldwide.

Uses & applications

Used historically for sharp stone tools and fire-starting; today it is mainly a teaching, archaeological, or collecting specimen, with chert also used locally as aggregate.

Geological facts

Fresh fracture surfaces can be glassy and sharp, while weathered surfaces become rough or chalky. Flint is generally a dark, compact variety of chert, often colored by organic matter or iron impurities.

Field identification & locations

Look for extreme hardness, fine texture, lack of visible grains, and shell-like fracture; it should scratch glass but not be scratched by a steel knife. Common locations include chalk and limestone regions, river gravels, and glacial deposits.