Limestone, travertine and marble are all forms of limestone. Limestone is a sedimentary rock composed of calcium carbonate fossils held together by dissolved minerals. It forms at the bottom of oceans and lakes. Travertine occurs when the hot water of geysers or mineral springs percolates up through limestone, bringing layers of dissolved minerals to the surface. Marble forms when natural heat and pressure build up on limestone, which then recrystallizes.
Travertine tiles are usually beige, cream or tan, with a swirling pattern, and additional colors and vein patterns occur depending on the specific mineral makeup of the stone. Because the stone is porous, with holes and troughs in its surface, it is often filled with concrete before polishing or honing. Unfilled travertine tile is also available and is most often used as an exterior surface. Travertine tiles most commonly come in large sizes for use as floor tiles. They are resistant to heat, scratching and staining.
Limestone tiles come in soft beige, cream, brown or tan, polished or natural. They are appropriate for bathrooms, fireplaces, countertops and flooring. Since limestone tiles don't have the pitting of travertine tiles, they don't need to be filled. They are heat-resistant and easy to clean and often used outdoors because of their porosity.
Because travertine is a soft stone, it is a difficult choice for flooring and requires special maintenance. Thus, it is most often used for building facades or cladding. It requires grinding to hone the surface, which sometimes reveals deeper holes in the rock, formed by gas bubbles. Limestone, while rugged and durable, scratches and stains easily.
Limestone is quarried in almost every state in the United States. Travertine, however, develops only where there are hot springs, such as Mammoth Hot Springs in Yellowstone National Park, and it can't be quarried there. Travertine also exists in Oklahoma and Texas. Most of the travertine in the U.S. is from Italy, where it has been used as a building material for centuries. In the past decade, travertine has been increasingly imported from other countries, including Iran, Mexico, Turkey and Peru.