Limestone is a sedimentary stone, primarily composed of calcium carbonate. As it was formed over time in clear, warm, shallow marine waters, it is embedded with ancient aquatic fossils. It is a soft, porous stone so it can be easily stained. Regular sealing is required. It is generally recommended for indoor use only and in applications where there is a lower chance of acid-wear, such as in bathrooms, on fireplaces and living room floors.