sedimentary

Chert (Jasper/Flint variety)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Tan, brown, and grey with possible iron oxide staining; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 7 on Mohs scale
Color: Tan, brown, and grey with possible iron oxide staining
Luster: Waxy to dull

Identified July 21, 2026More sedimentary →

Explore Chert (Jasper/Flint variety) 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 accumulation of silica-rich microfossils (like radiolaria or diatoms) or by chemical precipitation in marine or groundwater environments. Often found as nodules in limestone or chalk beds.

Uses & applications

Historically used for making stone tools (arrowheads/scrapers) due to conchoidal fracturing. Modern uses include road surfacing, decorative gravel, and lapidary work (polishing into cabochons).

Geological facts

Because it breaks with a very sharp edge, chert was one of the most important minerals for early human technological development. It is also sparks when struck against steel, making it vital for early fire-starting and flintlock firearms.

Field identification & locations

Identify by its waxy texture, extreme hardness (it will scratch glass), and the way it breaks into curved, shell-like (conchoidal) shards. Commonly found in creek beds or limestone outcrops.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Sedimentary Sandstone

Arenite (Sedimentary Rock)

sedimentary

Fossiliferous Concretion

Septarian Concretion containing Brachiopods/Crinoids

fossil

Shale

Shale (clastic sedimentary rock)

sedimentary

Brown Sandstone (River Rock)

Arenite

sedimentary

Shale

Argillaceous sedimentary rock

sedimentary