sedimentary

Chert

Microcrystalline quartz (SiO2)

Hardness of 7 on Mohs scale, earthy to waxy luster, conchoidal fracture, and typically colored light brown, tan, or gray.

Identified October 18, 2026More sedimentary →

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Physical properties

Hardness of 7 on Mohs scale, earthy to waxy luster, conchoidal fracture, and typically colored light brown, tan, or gray.

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 and arrowheads due to its sharp edges when fractured.

Chert forms nodules or layers within sedimentary rocks like chalk and limestone, and varieties include flint and jasper.

Identified by its extreme hardness, vitreous to dull luster, and distinct conchoidal fracture. Found worldwide in sedimentary formations.

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)