sedimentary

Limestone

Calcium carbonate (CaCO3)

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

Identified October 24, 2026More sedimentary →

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Physical properties

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

Formed by the accumulation of organic remains like shells and coral or chemical precipitation in shallow marine environments over millions of years.

Widely used in construction as building stone, aggregate in concrete, and in the production of cement and agriculture lime.

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

Easily identified by its characteristic effervescence when treated with dilute hydrochloric acid; 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)