Limestone

Limestone is a sedimentary rock composed mainly of calcium carbonate (CaCO3), usually in the form of the minerals calcite or aragonite. It forms primarily through the accumulation of calcareous remains of marine organisms such as corals and shells, but can also result from the precipitation of calcium carbonate from water in caves and hot springs.

Limestone textures vary and include fossiliferous, bioclastic, oolitic, and micritic varieties. Related forms include chalk and travertine. Impurities such as clay, silica, or iron oxides give color and influence texture. When magnesium-rich fluids alter limestone, dolostone can form; this is a dolomite rock rather than true limestone.

Geographically, limestone is widespread and forms in many environments, especially where shallow, warm seas once existed. Dissolution by carbonic acid in groundwater drives karst processes, creating features such as caves, sinkholes, and underground drainage systems.

Uses of limestone are diverse. It serves as a major building material and as a raw material for cement and lime. It is also used in aggregates for roads, for soil conditioning, in chemical processes, and as a decorative stone in architecture and sculpture.

Identification and properties typically include a gray to white color range, hardness around 3 on the Mohs scale, and a tendency to fizz when exposed to dilute acids due to its calcite content. It often forms porous or dense rocks with variable porosity and isSedimentary rock of considerable economic and geological importance.

Related rocks include chalk, travertine, and marble, the latter being a metamorphosed form of limestone.