sedimentary

Chert Pebble

Sedimentary cryptocrystalline quartz (SiO2)

Hardness of 7 on the Mohs scale, waxy luster, conchoidal fracture, and brownish-grey coloration with weathered cortex.

Identified October 19, 2026More sedimentary →

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Physical properties

Hardness of 7 on the Mohs scale, waxy luster, conchoidal fracture, and brownish-grey coloration with weathered cortex.

Formed through the chemical precipitation of silica in marine environments or replacement of limestone during the Cretaceous period.

Used primarily in landscaping, historical tool-making, and as a durable aggregate in construction.

Ancient humans prized chert for its ability to fracture into extremely sharp edges, making it ideal for arrowheads and cutting tools.

Identify in the field by its hardness, smooth water-worn surface, and distinct conchoidal fracture. Commonly found in riverbeds and gravel deposits.

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)