sedimentary

Chert

Microcrystalline quartz (SiO2)

Hardness of 7 on the Mohs scale, typically grey to brown, waxy to vitreous luster, amorphous crystal structure, and conchoidal fracture.

Identified November 2, 2026More sedimentary →

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Physical properties

Hardness of 7 on the Mohs scale, typically grey to brown, waxy to vitreous luster, amorphous crystal structure, and conchoidal fracture.

Formed through the chemical precipitation of silica from seawater or the replacement of limestone by silica-rich solutions over millions of years.

Historically used by early humans for making stone tools, arrowheads, and blades due to its sharp conchoidal fracture.

Also known as flint when dark-colored, chert was essential for ancient survival and fire-starting when struck against steel.

Identify by its extreme hardness, waxy luster, and sharp edges when fractured. Commonly found embedded in limestone or chalk 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

Fossiliferous Sedimentary Rock

Sedimentary limestone with invertebrate fossil imprint

Sandstone or Siltstone

Arenite (if sandstone)

Sandstone

Arenite

Shale

Shale (clastic sedimentary rock)

Shale (or Mudstone/Siltstone)

Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)