Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different
crystal forms of calcium carbonate (CaCO3). Many limestones are composed from 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 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, and as a chemical feedstock.
The first geologist to distinguish limestone from dolomite was Belsazar Hacquet in 1778.
Description[]
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 after the organisms die.
Limestone often contains variable amounts of silica in the form of chert (chalcedony, flint, jasper, etc.) or siliceous skeletal fragment (sponge spicules, diatoms, radiolarians), and varying amounts of clay, silt and sand (terrestrial detritus) carried in by rivers.
Trivia[]
- Limestone is very common in architecture, especially in Europe and North America.
- The Florida Keys, islands off the south coast of Florida, are composed mainly of oolitic limestone.
- It is often found in medicines and cosmetics.
- It is used in sculptures because of its suitability for carving.
- Some limestones do not consist of grains at all.