Limestone is formed over millions of years by accumulated shells and remains from hard organisms such as molluscs and corals. It is a sedimentary rock, meaning it was formed by water or wind deposits, and contains at least 50 per cent calcite (calcium carbonate). Other elements that make up the rock are determined by the place where the limestone was formed and can include clay, pyrite, quartz and feldspar. The wide array of shades, colours, textures and its durability make limestone a very popular stone for both traditional and contemporary interiors. Limestone tile textures available range from aged, brushed, honed, polished and tumbled, can be used for both walls and floors and so possess an ever expanding appeal. As it is reactive to acid solutions and so should only be cleaned with a neutral or mild alkaline-based cleaner.