sedimentary

Chert

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale), Color: tan to gray-green, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.6-2.7

Identified July 9, 2026More sedimentary →

Explore Chert 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 scale), Color: tan to gray-green, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.6-2.7

Formation & geological history

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

Uses & applications

Historically used for making sharp-edged tools (flintknapping) such as arrowheads and scrapers. Today used as a construction aggregate, for road surfacing, and as a decorative landscaping stone.

Geological facts

Because it is harder than steel and breaks with very sharp edges, it was one of the most important materials for early human technology. Flint is a well-known variety of chert.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), its waxy feel, and the way it breaks into curved, shell-like (conchoidal) surfaces with sharp edges. It is often found in river beds or weathering out of limestone cliffs.