Travertine

Travertine, whitish, porous or crystalline mineral form of calcium carbonate, deposited in layered formations by hot and cold spring waters. The compact variety of travertine has been used as building stone since ancient Roman times, and the porous variety, better known as tufa, is used today to line interior walls. Deposits of travertine in the U.S. are found in Yellowstone National Park in Wyoming and in California and Colorado, and massive deposits occur near Tivoli, Italy. The ornamental Mexican onyx, or onyx marble, is also a variety of travertine.