sedimentary

Limestone

Sedimentary rock composed primarily of Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Grey, beige, or white; Luster: Dull/Earthy; Crystal Structure: Usually microcrystalline (micrite); Cleavage: None (conchoidal to irregular fracture); Specific Gravity: 2.5–2.7

Hardness: 3 on Mohs scale
Color: Grey, beige, or white
Luster: Dull/Earthy

Identified July 19, 2026More sedimentary →

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Physical properties

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. Significant deposits date from the Paleozoic through the Cenozoic eras.

Uses & applications

Used extensively in construction as road base, railroad ballast, and building stone. It is the primary ingredient in Portland cement and is used as a soil conditioner in agriculture.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. Most of the world's major cave systems, such as Mammoth Cave, are formed in limestone beds due to their solubility in slightly acidic rainwater.

Field identification & locations

Can be identified in the field by its reaction to dilute hydrochloric acid (it will fizz/effervesce). Look for fossils of marine organisms. It is commonly found in areas that were once prehistoric seafloors.

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