sedimentary

Chert (Flint / Chalcedony nodule)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: brownish-gray, tan, waxy yellowish-brown; Luster: waxy to dull; Cleavage: none (conchoidal fracture); Specific Gravity: 2.5-2.7

Hardness: 6
Color: brownish-gray, tan, waxy yellowish-brown
Luster: waxy to dull

Identified November 15, 2026More sedimentary →

Explore Chert (Flint / Chalcedony nodule) in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 6.5-7 on Mohs scale; Color: brownish-gray, tan, waxy yellowish-brown; Luster: waxy to dull; Cleavage: none (conchoidal fracture); Specific Gravity: 2.5-2.7

Formation & geological history

Formed through the biochemical accumulation of siliceous organism remains (like diatoms, radiolarians, or sponge spicules) in marine sediments, or by precipitation/replacement of silica in limestone or chalk beds.

Uses & applications

Historically used for crafting stone tools, arrowheads, and striking fire due to its hardness and sharp conchoidal edges. Occasionally used in gravel, lapidary tumbling, or landscaping.

Geological facts

Because chert breaks with razor-sharp conchoidal fractures, it was one of the most critical materials for human technological development in the Stone Age.

Field identification & locations

Look for a smooth, waxy feel and rounded nodular form that easily scratches glass and steel without reacting to acid. Commonly found in river gravels, chalk or limestone formations, and glacial tills.