sedimentary

Limestone

Calcium Carbonate (CaCO3)

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

Identified October 31, 2026More sedimentary →

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Physical properties

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

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

Widely used in construction as building stone, as an aggregate for road bases, in the production of cement, and in agricultural soil conditioning.

Limestone frequently contains well-preserved fossils of ancient marine organisms and makes up about 10% of the total volume of all sedimentary rocks.

Easily identified in the field by its effervescence when exposed to acid and its soft, fine-grained texture; found worldwide in sedimentary basins.

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)