sedimentary

Limestone Concretion

Calcium Carbonate Concretion (CaCO3)

Hardness of 3 on the Mohs scale, brownish-orange weathered exterior, earthy to vitreous luster, amorphous to microcrystalline structure.

Identified October 29, 2026More sedimentary →

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Physical properties

Hardness of 3 on the Mohs scale, brownish-orange weathered exterior, earthy to vitreous luster, amorphous to microcrystalline structure.

Formed through the precipitation of mineral cement within the pores of sedimentary rocks, typically during early burial.

Used primarily in landscaping, decorative stone displays, and as educational geological specimens.

Concretions often form around a central nucleus such as a fossil fragment, leaf, or shell, creating unusual shapes as they weather out.

Easily identified by their distinct rounded or nodular shapes weathering out of softer surrounding sedimentary layers like shale or sandstone.

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)