sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale), Color: Charcoal grey to black, Luster: Waxy to dull, Crystal structure: Microcrystalline/Cryptocrystalline quartz, Cleavage: None (conchoidal fracture), Specific gravity: 2.65

Identified May 24, 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 precipitation of silica-rich fluids in sedimentary environments, often within limestone or chalk beds. It can also form from the accumulation of silica-based micro-fossils like radiolarians.

Uses & applications

Historically used for stone tools and starting fires; currently used in construction aggregate, road surfacing, and as high-quality flint for sparking in historical reenactments.

Geological facts

Chert has been used by humans for millions of years to create sharp-edged tools like arrowheads and axe heads because of its predictable conchoidal fracture pattern.

Field identification & locations

Identify in the field by its sharp, glass-like edges when broken and its ability to scratch glass. Often found in nodules within limestone or as river-worn cobbles.