A sedimentary rock composed of crystal forms of calcium carbonate, limestone is hard and durable, standing up well to exposure. It is hard and durable, but easily cut into large blocks or more elaborate carving. It has been used as a dimension stone for ages and many famous buildings in London are built from limestone. This material is available and in stock in 2 cm, 3 cm, and 5 cm slabs and various tile formats including 12" x 24", 24" x 24", 18" x 36", and 24" x 48".