sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Brown, grey, and waxy tan; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture).

Hardness: 7 on Mohs scale
Color: Brown, grey, and waxy tan
Luster: Dull to waxy

Identified July 7, 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

Hardness: 7 on Mohs scale; Color: Brown, grey, and waxy tan; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture).

Formation & geological history

Formed as nodules or layers in limestone or chalk through the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) that dissolve and reprecipitate as microcrystalline quartz.

Uses & applications

Historically used for stone tools and weapons due to sharp edges; currently used for road surfacing, flintlocks, and fire-starting kits.

Geological facts

Chert has a conchoidal fracture, meaning it breaks like glass to create razor-sharp edges. It was one of the most important minerals for prehistoric humans to create arrowheads and scrapers.

Field identification & locations

Look for a glassy or waxy texture on broken surfaces and a hardness that can scratch glass. It is commonly found in sedimentary basins or as rounded pebbles in riverbeds.