sedimentary

Chert

Silicon dioxide (Microcrystalline Quartz, $SiO_2$)

Hardness of 7 on the Mohs scale, typically gray, brown, or white in color, waxy to vitreous luster, cryptocrystalline or microcrystalline structure, exhibits conchoidal fracture with no true cleavage, specific gravity of 2.60 to 2.65.

Identified July 31, 2026More sedimentary →

Explore Chert 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

Forms in marine environments through the chemical precipitation of silica from silica-rich solutions or the accumulation of siliceous skeletal remains of organisms such as radiolarians and diatoms, typically within limestone or chalk formations.

Uses & applications

Historically used extensively by early humans for making stone tools, arrowheads, and blades due to its conchoidal fracture. Also used historically for striking fire with steel, and in modern times occasionally used as road aggregate or ornamental landscaping stone.

Geological facts

Chert is a hard, tough sedimentary rock that breaks with sharp edges. Varieties of chert include flint, jasper, and chalcedony depending on color and impurities.

Field identification & locations

Can be identified in the field by its extreme hardness (scratches glass), waxy luster, and distinctive conchoidal fracture surfaces. Commonly found embedded as nodules or layers within chalk or limestone formations worldwide.

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

Banded Siltstone / Mudstone Pebble

Siltstone / Argillite

sedimentary

Shale (or Mudstone/Siltstone)

Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)

sedimentary

Shale

Shale (clastic sedimentary rock)

sedimentary