sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Tan, beige, or gray; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).

Hardness: 7 on Mohs scale
Color: Tan, beige, or gray
Luster: Dull to waxy

Identified May 25, 2026More sedimentary →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 7 on Mohs scale; Color: Tan, beige, or gray; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).

Formation & geological history

Formed through the accumulation of silica-rich microfossils or precipitation from silica-rich fluids within limestone or chalk beds, often from the Paleozoic to Mesozoic eras.

Uses & applications

Used historically for stone tools and weapons (arrowheads); currently used in road construction, as an abrasive, and for fire-starting (flint).

Geological facts

Chert is so hard it can scratch steel. It was one of the first materials utilized by prehistoric humans due to its ability to break into extremely sharp edges.

Field identification & locations

Identify by its smooth, shell-like (conchoidal) fracture and its ability to scratch glass. Commonly found in riverbeds, limestone outcrops, and coastal areas.