Calcium carbonate deposited by precipitation from carbonate-saturated waters, particularly from hot springs. Travertine deposits are sometimes massive, but often display a concentric or fibrous internal structure, sometimes building large, concentric, spherical masses. Travertine is also found in cave deposits in the form of stalagmites and stalactites. A porous, sponge-textured form of travertine is referred to as ‘tufa’ or ‘calc-sinter’.