Limestone is a sedimentary rock composed largely of the minerals calcite andaragonite, which are different crystal forms of calcium carbonate (CaCO₃). Most limestone is composed of skeletal fragments of marine organisms such as coral or foraminifera.

Limestone makes up about 10% of the total volume of all sedimentary rocks. The solubility of limestone in water and weak acid solutions leads to karstlandscapes, in which water erodes the limestone over thousands to millions of years. Most cave systems are through limestone bedrock.

Limestone has numerous uses: as a building material, as aggregate for the base of roads, as white pigment or filler in products such as toothpaste orpaints, and as a chemical feedstock.