sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3-4 (Mohs); Color: Gray, tan, or white; Luster: Dull to earthy; Fine-grained texture; Fizzes when in contact with diluted hydrochloric acid.

Hardness: 3-4 (Mohs)
Color: Gray, tan, or white
Luster: Dull to earthy

Identified July 14, 2026More sedimentary →

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Physical properties

Hardness: 3-4 (Mohs); Color: Gray, tan, or white; Luster: Dull to earthy; Fine-grained texture; Fizzes when in contact with diluted hydrochloric acid.

Formation & geological history

Formed in marine environments through 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 for road base, concrete aggregate, and building stone. Also used as a flux in steel making and in the production of cement and lime.

Geological facts

Limestone is the primary source of the world's lime. It often contains fossils of ancient marine organisms, providing evidence of Earth's biological and environmental history.

Field identification & locations

Identify in the field by its gray color and easy scratching with a steel nail. The acid test (bubbling with vinegar or HCl) is definitive. Found globally in areas that were once prehistoric seafloors.