sedimentary

Limestone

Calcium Carbonate (CaCO3)

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

Identified November 8, 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 fine-grained crystal structure.

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

Extensively used in construction as building material, crushed stone for road base, and as a primary ingredient in cement production.

Limestone often contains well-preserved fossils and can dissolve slightly in acidic water to form spectacular cave systems and sinkholes.

Easily identified by its reaction to dilute hydrochloric acid, which causes it to effervesce and fizz vigorously.

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)