Travertine, a natural stone, is a white concretionary form of calcium carbonate that is usually hard and semi crystalline. It is deposited from the water of mineral springs (especially hot springs) or streams holding lime in solution. Extensive deposits exist at Tivoli, Italy, near Rome.
Travertine is sometimes known as travertine limestone, sometimes as traverline marble; these are the same stone even though it is neither limestone nor marble. The stone is characterised by pitted holes and troughs in its surface. While these troughs occur naturally they suggest to some eyes that considerable wear and tear has occurred over many years. Some installers use a grout to fill these holes, while others leave them open. It can be polished to quite a good degree of smoothness and shininess. Many colours are available from grey to a coral red. It is most commonly available in a tile size for interior flooring rather than in flagstone size for exterior paving.