sedimentary

Chert or flint fragment

Microcrystalline quartz (SiO₂), commonly called chert; darker varieties are termed flint

AI-generated identification · may be incorrect

Typically hardness 6.5–7, waxy to dull luster, opaque gray-brown coloration, and conchoidal fracture without visible crystals or cleavage. The specimen appears weathered and partly translucent at thin edges, consistent with silica-rich chert.

Identified August 28, 2026More sedimentary →

Explore Chert or flint 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

Forms by replacement or accumulation of microscopic silica in marine limestone, chalk, or sedimentary beds, commonly during the Paleozoic–Cenozoic eras. Exact age and source cannot be determined from the photograph.

Uses & applications

Used historically for sharp-edged tools and fire-making; crushed chert is used as aggregate and occasionally as a decorative stone. Small natural pieces generally have little commercial value.

Geological facts

Chert fractures into very sharp edges because of its quartz-rich composition. Flint is essentially a dark, compact form of chert, often associated with chalk deposits.

Field identification & locations

Identify it by its glassy or waxy surface, conchoidal fracture, lack of cleavage, and inability to scratch it with a steel knife easily; a streak test is usually white. Common in limestone, chalk, river gravels, and glacial deposits worldwide.