Limestone is a sedimentary rock composed largely of mineral calcite, the balance being made up by silica, flint, sand and clay. The primary source of calcite is most commonly marine organisms. Limestone is quarried from places, which millions of years ago, would have formed the floor of a shallow area of the sea, often capturing fossilized plant and animal life. Like marble, Limestone is of a calcium carbonate base, and as such, is vulnerable to alteration by exposure to mild acids.
