sedimentary

Limestone

Calcium carbonate (CaCO3)

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

Formed through the accumulation and compaction of organic remains like shells and coral in shallow marine environments over millions of years.

Widely used in construction for concrete and road base, in agriculture to neutralize soil acidity, and in the manufacturing of cement and lime.

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

Can be easily identified in the field by its characteristic reaction to dilute hydrochloric acid, which causes it to fizz and release carbon dioxide.

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)