sedimentary

Limestone

Calcium Carbonate (CaCO3)

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

Identified October 23, 2026More sedimentary →

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Physical properties

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

Formed through the accumulation of shell, coral, algal, and fecal debris, or chemical precipitation, primarily in shallow marine environments.

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

Limestone frequently contains well-preserved fossils of ancient marine organisms and forms spectacular cave systems via dissolution.

Identify in the field by its characteristic pale color, softer composition, and a vigorous fizzing reaction when exposed to acid.

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)