sedimentary

Chert (varietal Flint)

Chert (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs; Color: Gray, white, or beige; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 Mohs
Color: Gray, white, or beige
Luster: Waxy to dull

Identified May 3, 2026More sedimentary →

Explore Chert (varietal Flint) in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 7 Mohs; Color: Gray, white, or beige; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed by the precipitation of microcrystalline silica from water, often replacing organic material or filling cavities in limestone/chalk. Found in formations from the Precambrian to Cenozoic eras.

Uses & applications

Historically used for stone tools and weapons (arrowheads); currently used as a road aggregate, in glass making, and as decorative gravel.

Geological facts

Flint is a variety of chert that occurs in chalk or marly limestone. It was the most important material for early human tool development because of how it breaks into sharp edges.

Field identification & locations

Identify by its characteristic conchoidal (shell-like) fracture and ability to scratch glass. Commonly found as nodules in riverbeds or limestone outcroppings.