Travertine is a seimentary rock. It is a natural chemical precipitate of carbonate minerals; typically Aragonite, but often recrystallized to or primarily Calcite. Basically calcium carbonate is deposited from the water of mineral springs or rivulets saturated with calcium bicarbonate. The spring water can either be hot, warm or cold. The amount of deposits may increase with the waters temperature or when biotic material accelerates the precipitation.