sedimentary

Chert (often called Flint or Jasper)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale), Color: dull yellowish-green to gray with dark inclusions, Luster: waxy to vitreous, Crystal Structure: Cryptocrystalline (microscopic), Cleavage: None (it has conchoidal fracture), Specific Gravity: 2.65

Identified April 24, 2026More sedimentary →

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 precipitation of silica-rich fluids within sedimentary rock layers, often replacing limestone or forming as nodules. It commonly originates from the accumulation of microscopic skeletal remains of marine organisms like diatoms and radiolarians.

Uses & applications

Historically used for making stone tools and starting fires (flint). Currently used as an industrial abrasive, road surfacing material, and occasionally for lapidary work or semi-precious jewelry when vibrantly colored.

Geological facts

Because of its extreme hardness and conchoidal fracture, chert was the most common material used by prehistoric humans to create sharp-edged tools like arrowheads, scrapers, and knives.

Field identification & locations

Identify in the field by its smooth, waxy surface and its tendency to break with sharp, curved 'shell-like' edges (conchoidal fracture). It will scratch glass easily but cannot be scratched by a steel knife. Commonly found in riverbeds and limestone outcrops.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Sandstone

Arenite (primarily SiO2)

sedimentary

Chert Breccia

Brecciated Chert (Microcrystalline Silica)

sedimentary

Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

sedimentary

Shale or Slaty Mudstone

Argillaceous sedimentary rock

sedimentary

Sandstone

Arenite

sedimentary