Most of the time, marble and granite can be identified by visible particles at the surface of the stone. Marble has veining, and granite has a flecked or granular appearance. Natural stone is categorized into two general categories according to its composition: Siliceous stone is composed mainly of silica- or quartz-like particles and tends to be very durable and easy to clean. Included in this category are granite, slate, and sandstone. Calcareous stone is composed mainly of calcium carbonate. It is sensitive to acidic cleaning products and frequently requires different cleaning procedures than siliceous stone. These types of stones include marble, travertine, limestone, & onyx.