sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness 7 on the Mohs scale; color ranges from grey, brown, to translucent smoke; waxy to vitreous luster; cryptocrystalline structure; conchoidal fracture with sharp edges; specific gravity around 2.5 - 2.8.

Identified October 26, 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 diagenetic precipitation of biochemical silica (from radiolarians, diatoms, or sponge spicules) within marine or lacustrine sedimentary rocks, typically found as nodules or bedded formations in limestone and chalk.

Uses & applications

Historically used for making stone tools, arrowheads, and spark-generating flint-and-steel strikers. Today used in gravel aggregates, road metal, and occasionally tumbled for lapidary use.

Geological facts

Because chert breaks with extremely sharp, smooth conchoidal edges, prehistoric humans prized it globally for crafting cutting tools and weapons. Its ability to create sparks when struck against iron or pyrite was essential for starting fires.

Field identification & locations

Recognized by its smooth waxy surface, extreme hardness (scratches glass/steel easily), lack of cleavage, and sharp, curving shell-like fracture planes. Extremely common in river gravels, limestone quarries, and beaches worldwide.