sedimentary

Chert (Flint nodule)

Microcrystalline / Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness 7 on the Mohs scale; conchoidal fracture with sharp edges; waxy to dull luster; grey to brownish-grey interior with a rough, light-colored chalky weathered exterior cortex; dense with specific gravity around 2.6.

Identified November 15, 2026More sedimentary →

Explore Chert (Flint nodule) 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 biochemically or diagenetically within marine sedimentary rocks (often limestone or chalk) as silica precipitates and replaces carbonate material, frequently aggregating around organic matter.

Uses & applications

Historically used for Stone Age tools (arrowheads, scrapers) and strike-a-light fire starters; modern uses include construction aggregate, road base, and decorative stone.

Geological facts

Flint was one of the very first minerals actively mined by early humans during the Neolithic period. Its predictable conchoidal fracture allowed precise knapping into razor-sharp hunting implements.

Field identification & locations

Identifiable by its sharp, curved conchoidal fracture surfaces, ability to easily scratch glass (Mohs 7), resistance to dilute acids, and characteristic chalky outer rind (cortex). Common globally in chalk cliffs, limestone beds, and river gravels.