Limestone is a sedimentary rock composed largely of calcite, calcium carbonate (CaCO3). Limestone often contains variable amounts of silica or siliceous skeletal fragment, as well as varying amounts of clay, silt and sand sized terrestrial detritus carried in by rivers. Limestone was also a very popular building block in the Middle Ages in the areas where it occurred, since it is hard, durable, and commonly occurs in easily accessible surface exposures. Many medieval churches and castles in Europe Read more [...]