Limestone is a widely occurring sedimentary rock composed mainly of calcium carbonate (CaCO₃), typically in the form of the mineral calcite. It generally contains more than 50% calcium carbonate, giving it its distinctive properties and making it an essential raw material in numerous industries. Limestone forms through various natural processes and therefore exists in multiple types with unique characteristics and textures.

This rock may be chemically precipitated from water, forming non-clastic and inorganic limestone, or develop biologically through marine life activities. Many limestones are produced when corals, algae, and other sea organisms secrete calcium carbonate, or when shells and skeletal remains of marine creatures accumulate and compact over millions of years — forming bioclastic or biochemical limestone. Some varieties emerge from the cementation of sand and mud by calcite, creating clastic limestone types that can resemble sandstone or mudstone in appearance.