sedimentary

Limestone

Calcium carbonate (CaCO3)

Hardness of 3 on the Mohs scale, typically gray, white, or tan with a dull to earthy luster and a fine-grained crystal structure.

Identified October 20, 2026More sedimentary →

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Physical properties

Hardness of 3 on the Mohs scale, typically gray, white, or tan with a dull to earthy luster and a fine-grained crystal structure.

Formed through the accumulation of shell, coral, algal, and fecal debris, often in shallow marine environments over millions of years.

Extensively used in construction, as a primary component of Portland cement, and in agriculture to neutralize acidic soils.

Limestone frequently contains well-preserved fossils and dissolves slowly in acidic water, creating extensive cave systems and karst topography.

Easily identified by its characteristic fizz when tested with dilute hydrochloric acid; found globally 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)