Travertine is a form of limestone deposited by mineral springs, especially hot springs. Travertine usually 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. It is frequently used as a building material such as walls and floors. It is also popular for the use of vanity tops, fireplace surrounds, thresholds etc. Often times, larger pits and holes are filled before being imported by the suppliers with an epoxy.