sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: typically white, gray, or tan; Luster: dull to earthy; Structure: non-crystalline or microcrystalline (fine-grained); Cleavage: none in bulk rock form; Reacts with dilute hydrochloric acid.

Hardness: 3 on Mohs scale
Color: typically white, gray, or tan
Luster: dull to earthy

Identified April 9, 2026More sedimentary →

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Physical properties

Formation & geological history

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

Uses & applications

Extensively used as a building material, in the manufacturing of cement (Portland cement), as an aggregate for the base of roads, as a white pigment/filler in products like toothpaste, and as a soil conditioner in agriculture.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary parent material for karst landscapes, which include caves, sinkholes, and underground rivers.

Field identification & locations

Identify in the field by testing with a drop of vinegar or diluted HCl; it will effervesce (fizz). Look for a relatively soft, light-colored rock that may contain small fossil fragments. It is common globally in areas that were once prehistoric seafloors.