Travertine is a form of limestone deposited by mineral springs. Travertine often has a fibrous or concentric appearance and exists in white, tan, cream-colored, and even rusty varieties.  It is formed by a process of rapid precipitation of calcium carbonate, often at the mouth of a hot spring or in a limestone cave. In the latter, it can form stalactites, stalagmites, and other speleothems. Travertine is a terrestrial sedimentary rock, formed by the precipitation of carbonate minerals from solution in ground and surface waters, and/or geothermally heated hot-springs.