Travertine is a type of limestone but differs in that it formed in a hot springs called karst. The water movement in this karst erodes the travertine creating holes in the stone. Polished travertine will usually have these holes filled with colored cement. These fillers typically are not polished and will give the travertine a blotchy appearance. Unfilled travertine will exhibit these holes and are commonly found on walls, floors, and building exteriors. Travertine is commonly found in tans and beige colors but can also be found in silver and reds.