sedimentary

Chert (Flint/Jasper)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale), Color: tan, grey, brown, or white; Luster: waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.5-2.8

Hardness: 6
Color: tan, grey, brown, or white
Luster: waxy to dull

Identified May 24, 2026More sedimentary →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 6.5-7 (Mohs scale), Color: tan, grey, brown, or white; Luster: waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.5-2.8

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation within sedimentary rocks like limestone or dolomite, typically in marine environments.

Uses & applications

Historically used for stone tools and weapons (arrowheads); currently used as a raw material for road construction, landscape stone, and occasionally in jewelry for polished stones.

Geological facts

Because it breaks with a conchoidal fracture, it produces very sharp edges. It was the primary material for the Stone Age tool industry. It can also produce sparks when struck against steel.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel nail) and the shell-like (conchoidal) curves where it is broken. Often found as nodules within limestone outcrops or as river pebbles.