travertine  
Travertine is a sedimentary calciferous stone formed in hot springs. Typically, hot water passes through limestone beds and takes the calcium from the limestone into suspension and takes that solution to the surface where the water evaporates and leaves the calcium crystals in layers on the surface. Travertine can be filled, usually with a cement filler or left unfilled for a more rustic appearance.
Durango Ancient Viejo™