Travertine is really a type of limestone. It is actually the terrestrial (land) formed version of limestone, as opposed to the marine based formations of many other limestone varieties. Travertine, like marble, is of a calcium carbonate base, and as such, are vulnerable to alteration by exposure to mild acids. A wide variety of stones are included in this group, and absorption varies from slight (<1%) to high (>10%). The combination of acid sensitivity and absorption limit the number of varieties that are suitable for countertop applications, and the user of limestone countertops should be well educated in its properties to accurately anticipate its behavior in service.