sedimentary

Gray flint or chert fragment

Microcrystalline quartz (SiO₂), likely chert/flint

AI-generated identification · may be incorrect

Opaque medium-gray, dull to slightly waxy luster, very fine-grained cryptocrystalline structure, and conchoidal fracture; Mohs hardness about 7. The image appears to show a naturally fractured or cut fragment on a pale stone-like surface.

Identified August 22, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms by silica replacement or accumulation in marine or freshwater sediments, commonly during the Paleozoic–Cenozoic; exact age cannot be determined visually. The dark gray color may reflect organic matter or minor iron/manganese impurities.

Uses & applications

Used historically for sharp tools, fire-starting, and arrowheads; attractive pieces may be polished for décor or collecting. Ordinary fragments generally have minimal market value.

Geological facts

Chert and flint are compositionally similar varieties of microcrystalline quartz; flint commonly denotes dark, nodular chert. It can produce a sharp edge and sparks against steel.

Field identification & locations

Identify it by hardness, inability to scratch it with steel, and smooth curved fracture surfaces; it should not fizz in dilute hydrochloric acid. Common in limestone formations worldwide, including the United States, Europe, and Australia.