Travertine is a natural stone such as Marble, Granite, Onyx, Limestone, Slate etc. The key difference between Travertine and other natural stones lies in the formation of the rock, the hardness of the stone and the appearance. Travertine is formed in hot springs and/or limestone caves. Travertine is not the same as Marble or Limestone which falls in the metamorphic rock category. Key characteristics of Travertine stone are the holes within the stone which are caused by carbon dioxide evasion.