sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness of 3 on the Mohs scale, grayish to white color, dull to earthy luster, and effervesces strongly in dilute hydrochloric acid.

Identified October 23, 2026More sedimentary →

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Physical properties

Hardness of 3 on the Mohs scale, grayish to white color, dull to earthy luster, and effervesces strongly in dilute hydrochloric acid.

Formed from the accumulation of skeletal fragments, coral, algal, and fecal debris in shallow marine environments over millions of years.

Extensively used in construction as building material, road base, aggregate, and in the production of cement and agricultural lime.

Limestone frequently contains well-preserved fossils and forms dramatic karst topography, including extensive cave systems and sinkholes.

Identified by its characteristic softness and strong reaction to acid; found globally in regions with ancient marine depositional histories.

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)