Sedimentary

Chert

Silicon dioxide (SiO2)

Hardness 6.5-7 on Mohs scale, typically occurs in massive form. Conchoidal fracture. Color can vary widely; this piece shows tan, light brown, and gray hues. Waxy to dull luster.

Identified April 26, 2026More sedimentary →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness 6.5-7 on Mohs scale, typically occurs in massive form. Conchoidal fracture. Color can vary widely; this piece shows tan, light brown, and gray hues. Waxy to dull luster.

Formation & geological history

Formed as a chemical sedimentary rock, typically from the precipitation of silica from groundwater or oceanic water, often replacing other minerals or organic material.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its conchoidal fracture. Sometimes used as a low-grade road material or collected as a specimen.

Geological facts

Flint is a type of chert that occurs specifically in chalk or marly limestone deposits. The sharp edges produced when fractured made it invaluable to early humans.

Field identification & locations

Identified by its waxy luster, hardness (scratches glass), and conchoidal fracture. Often found as nodules in limestone or as layered deposits. Look for smooth, curved broken surfaces.