Limestone is a sedimentary rock, which means it was formed from small particles of rock or stone that have been compacted by pressure. Because limestone is often formed from shells and bones, it is a light color like white, tan, or gray. The color of the limestone depends on the other sediments in the mixture besides the mineral calcite, which is white; impurities such as sand, clay, and organic material are also present in limestone and affect the color. The skeletal fragments of marine organisms visible on limestone countertops create a very unique surface. Due to their fragility and susceptibility to scratching, staining, and etching, limestone countertops are best suited for low-traffic areas.