Coralline limestone

Limestone

Sedimentary rock
Limestone outcrop in the Torcal de Antequera nature reserve of Málaga, Spain
Composition
Calcium carbonate: inorganic crystalline calcite and/or organic calcareous material

Limestone is a sedimentary rock, composed mainly of skeletal fragments of marine organisms such as coral, forams and molluscs. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO₃).

About 10% of sedimentary rocks are limestones. The solubility of limestone in water and weak acid solutions leads to karst landscapes, 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 or paints, as a chemical for the production of lime, as a soil conditioner, or as a popular decorative addition to rock gardens.

The first geologist to distinguish limestone from dolomite was Belsazar Hacquet in 1778.

Like most other sedimentary rocks, most limestone is composed of grains. Most grains in limestone are skeletal fragments of marine organisms such as coral or foraminifera. Other carbonate grains comprising limestones are ooids, peloids, intraclasts, and extraclasts. These organisms secrete shells made of aragonite or calcite, and leave these shells behind when they die.