sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: White, grey, light blue-grey; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: White, grey, light blue-grey
Luster: Waxy to dull

Identified July 1, 2026More sedimentary →

Explore Chert (Flint) 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

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation in marine environments. Often found as nodules within limestone or chalk beds.

Uses & applications

Historically used for stone tools and weapons due to sharp edges; currently used as road aggregate, in glass manufacturing, and occasionally in jewelry as a cabochon.

Geological facts

Chert has a conchoidal fracture, which means it breaks like glass, producing sharp, curved edges. This property made it the primary material for arrowheads and spear points for thousands of years.

Field identification & locations

Identify by its hardness (it can scratch glass), its waxy texture, and the distinctive curved 'shell-like' patterns where it has been chipped. Commonly found in stream beds or within sedimentary rock outcrops.