Perhaps we should begin by defining a rock. Rock considered sedimentary is composed of particles that have been carried along and deposited by wind or water. Over time they become pressed together to form rocks. Metamorphic rock is formed when chemical reactions, heat, or pressure, or a combination of these, forces existing rock into new kinds of rock. The new rocks have different physical and chemical properties from the original rocks.
Organic rocks come from living organisms.
Deposits of limestone are typically derived from the shells of creatures such as clams and certain microorganisms. Limestone, onyx, and travertine are all in the family of organic rock. In the stone industry, rock can be classified by geologic classes or groups. Granites are typically harder, denser, and more durable than calcareous stones, which are more vulnerable to common domestic acids, such as orange juice, milk and vinegar. Many homebuyers considering the use of natural stone ask whether marble, limestone, travertine, and onyx are porous, vulnerable to staining, water absorption, and scratching.