sedimentary

Flint (chert) nodule

Microcrystalline quartz (SiO₂), occurring as a flint/chert nodule in limestone

AI-generated identification · may be incorrect

Dark gray-blue, waxy to dull luster, with a pale weathered cortex and rusty staining. Hardness about 7 Mohs; microcrystalline, with no visible cleavage and conchoidal fracture. The broken cavity may expose a fossil or mineral-filled interior.

Identified October 3, 2026More sedimentary →

Explore Flint (chert) 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

Silica-rich material replaced or accumulated within sedimentary rock, commonly forming nodules in chalk or limestone. Flint nodules are typically Cretaceous in age, though age depends on the host deposit.

Uses & applications

Historically important for stone tools and fire-starting; today used for teaching, collecting, and occasionally decorative work.

Geological facts

Flint’s sharp conchoidal edges made it a major prehistoric tool material. The image shows a nodule in its surrounding host rock, but the cavity’s contents are not clear enough to identify confidently.

Field identification & locations

Look for very hard, fine-grained material, a smooth curved fracture, and a contrasting chalky or weathered rind; common in chalk and limestone regions. Avoid assuming the cavity is a fossil without closer examination.