sedimentary

Chert

Microcrystalline quartz (SiO2)

Hardness of 7 on the Mohs scale, dull to waxy luster, conchoidal fracture, and colors ranging from white to gray and brown.

Identified November 13, 2026More sedimentary →

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Physical properties

Hardness of 7 on the Mohs scale, dull to waxy luster, conchoidal fracture, and colors ranging from white to gray and brown.

Formed through the chemical precipitation of silica from seawater or the replacement of limestone during sedimentary diagenesis.

Historically used for making stone tools and arrowheads due to its sharp edges when fractured.

Chert weathers into a chalky outer rind known as cortex and has been utilized by humans for over two million years.

Identify by its extreme hardness, smooth conchoidal fracture, and waxy appearance. Commonly found within chalk or limestone formations worldwide.

Fossil-bearing concretion, possibly containing a fossil shell or other organic inclusion

Calcareous concretion; exact fossil and host-rock composition are not identifiable from the image

Sandstone or Siltstone

Arenite (if sandstone)

Fossiliferous Sedimentary Rock

Sedimentary limestone with invertebrate fossil imprint

Shale

Fissile Sedimentary Rock

Sandstone

Arenite

Shale

Clastic sedimentary rock