sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 (Mohs scale), Color: Grey, Luster: Dull to earthy, Structure: Fine-grained/Microcrystalline, Cleavage: None (conchoidal or irregular fracture)

Identified July 19, 2026More sedimentary →

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Physical properties

Hardness: 3 (Mohs scale), Color: Grey, Luster: Dull to earthy, Structure: Fine-grained/Microcrystalline, Cleavage: None (conchoidal or irregular fracture)

Formation & geological history

Formed in marine environments from the accumulation of shell, coral, algal, and fecal debris. It can also be formed by the chemical precipitation of calcium carbonate from lake or ocean water.

Uses & applications

Used widely in construction (concrete), architecture, agriculture to neutralize acid soil, and as a raw material in the manufacturing of glass and steel.

Geological facts

Limestone covers about 10% of the total surface area of the Earth. It is the primary rock found in karst landscapes, where it dissolves to form caves and sinkholes.

Field identification & locations

Can be identified by a fizzing reaction when exposed to a drop of dilute hydrochloric acid (vinegar may cause a weak reaction). Look for visible fossils or a fine-grained, uniform grey texture.