Limestone is a member of the sedimentary rock family and is usually gray or black. Its chemical composition is mainly CaO, generally 45% to 55%, followed by a few of MgO, SiO 2 and Al 2 O 3.. The mineral composition of limestone rock is mainly calcite or calcareous bioclasts (such as shells or biological bones, which are also composed of calcium carbonate), followed by dolomite, clay, silt ...