sedimentary

Limestone

Limestone (CaCO3)

Hardness: 3-4 (Mohs scale), Color: Cream, grey, or tan, Luster: Dull to earthy, Structure: Massive or bedded, Cleavage: None (conchoidal fracture), Specific Gravity: 2.3-2.7

Identified July 21, 2026More sedimentary →

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Physical properties

Hardness: 3-4 (Mohs scale), Color: Cream, grey, or tan, Luster: Dull to earthy, Structure: Massive or bedded, Cleavage: None (conchoidal fracture), Specific Gravity: 2.3-2.7

Formation & geological history

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

Uses & applications

Widely used in construction as building stone, road base, and a key ingredient in portland cement and lime. Also used as a soil conditioner and in the manufacture of glass and paper.

Geological facts

Approximately 10% of the total volume of all sedimentary rocks on Earth is limestone. It is the primary rock found in karst landscapes, which feature caves, sinkholes, and underground rivers.

Field identification & locations

Identified in the field by its softness (can be scratched by a penny) and its strong reaction (effervescence) when touched by a drop of dilute hydrochloric acid. Commonly found in areas that were ancient seabed.