sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness of 3 on the Mohs scale. Color ranges from white, gray, yellow, to tan. Luster is typically earthy to dull. Crystal structure is microcrystalline or fine-grained. Exhibits good cleavage in three directions (rhombohedral) if crystalline, and effervesces (fizzes) when exposed to weak hydrochloric acid.

Identified August 1, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of skeletal fragments of marine organisms such as coral, algal, and molluscan remains, as well as the precipitation of calcium carbonate from water. Typically forms in shallow, calm, warm marine waters over millions of years.

Uses & applications

Widely used as a building material, an aggregate for road bases, a primary component of Portland cement, and in agriculture for neutralizing acidic soils.

Geological facts

Limestone frequently contains fossils of ancient marine life. Famous architectural structures like the Great Pyramids of Giza and parts of the Empire State Building utilize limestone.

Field identification & locations

Easily identifiable in the field by its light color and characteristic fizzing reaction with acid. Common worldwide in sedimentary basins, cliffs, and quarries.