sedimentary

Flint or chert fragment

Microcrystalline quartz (SiO₂), commonly with chalcedony and impurities

AI-generated identification · may be incorrect

Typically Mohs hardness 6.5–7, dull to waxy luster, gray-brown color, and conchoidal fracture producing sharp edges; no visible cleavage. The pale, chalky cortex suggests an outer weathering rind or residual host material.

Identified August 16, 2026More sedimentary →

Explore Flint or chert fragment in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Chert forms when silica precipitates or replaces sediment, often in limestone or chalk, during diagenesis; its exact age cannot be determined from the image. It occurs in sedimentary sequences ranging from Precambrian to Recent geological ages.

Uses & applications

Used historically for tools, fire-starting, and arrowheads; crushed chert is used as aggregate and road material. Attractive patterned pieces may be collected, but this fragment has little commercial value.

Geological facts

The curved, glasslike fracture and very fine texture are characteristic of flint/chert. A sharp edge and lack of visible grains distinguish it from ordinary sandstone.

Field identification & locations

Common in chalk and limestone regions, including parts of Europe, North America, and the Middle East. Field tests include scratching glass, observing conchoidal fracture, and checking that it does not fizz strongly in dilute acid.