sedimentary

Likely river-worn chert (flint) pebble

Microcrystalline quartz (SiO₂), commonly called chert or flint

AI-generated identification · may be incorrect

Dull to waxy gray-brown surface with rounded, water-worn shape; chert has Mohs hardness about 7, no visible crystal structure, and conchoidal fracture. The image alone cannot confirm its composition.

Identified October 11, 2026More sedimentary →

Explore Likely river-worn chert (flint) pebble in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Dull to waxy gray-brown surface with rounded, water-worn shape; chert has Mohs hardness about 7, no visible crystal structure, and conchoidal fracture. The image alone cannot confirm its composition.

Formation & geological history

Chert forms when silica accumulates and hardens in sedimentary settings, often replacing carbonate material; its age depends on the source bed. The pebble was likely rounded through transport in water.

Uses & applications

Chert has historically been used for tools and fire-starting; attractive pieces are kept as modest geological curiosities.

Geological facts

A fresh break typically shows smooth, curved conchoidal surfaces and sharp edges, a property that made chert valuable for prehistoric cutting tools.

Field identification & locations

Look for hardness sufficient to scratch glass and a waxy surface; common in river gravels and sedimentary regions worldwide. This specimen’s appearance is consistent with chert, but identification from the photo is uncertain.