sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness of 3 on Mohs scale, typically gray or tan in color, dull to earthy luster, and reacts strongly with dilute hydrochloric acid.

Identified October 22, 2026More sedimentary →

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Physical properties

Hardness of 3 on Mohs scale, typically gray or tan in color, dull to earthy luster, and reacts strongly with dilute hydrochloric acid.

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

Widely used in construction as aggregate for road base, as a primary component in manufacturing cement, and in agricultural soil treatment.

Limestone often preserves a rich fossil record of ancient marine life and is the primary rock type that forms extensive cave systems via dissolution.

Identified easily by its light color, fine-grained texture, and characteristic fizz when tested with an acid dropper.

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)