sedimentary

Chert

Microcrystalline Quartz (SiO2)

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

Identified October 18, 2026More sedimentary →

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Physical properties

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

Formed via the chemical precipitation of silica from aqueous solutions or the accumulation of siliceous microfossil skeletons in marine environments.

Historically utilized by humans for sharp-edged stone tools and weaponry; currently used in aggregate, abrasives, and historically for fire-starting.

Chert is exceptionally durable and resistant to weathering, often surviving as residual pebbles long after enclosing limestone has eroded away.

Identify in the field by its distinct conchoidal fracture, sharp edges when broken, and high hardness that scratches glass easily.

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)