sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3-4 (Mohs scale); Color: Gray, tan, or white; Luster: Dull to earthy; Texture: Fine-grained to clastic; Effervesces with dilute acid.

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

Identified July 14, 2026More sedimentary →

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Physical properties

Hardness: 3-4 (Mohs scale); Color: Gray, tan, or white; Luster: Dull to earthy; Texture: Fine-grained to clastic; Effervesces with dilute acid.

Formation & geological history

Formed primarily from the accumulation of shell, coral, algal, and fecal debris in marine environments. It can also form chemically through the precipitation of calcium carbonate from lake or ocean water.

Uses & applications

Used extensively in construction as aggregate, road base, and a component in cement. Also used in agriculture to neutralize soil acidity and in the production of lime.

Geological facts

Limestone is the primary rock type found in karst landscapes, leading to the formation of caves, sinkholes, and underground rivers because it is soluble in weak acids.

Field identification & locations

Identify in the field by testing with a drop of vinegar (it will bubble) and its relatively soft surface that can be scratched by a steel knife. Commonly found in areas that were once prehistoric seafloors.