Travertine is a sedimentary rock formed by the chemical precipitation of calcium carbonate minerals from fresh water,  typically in springs, rivers, and lakes; that is, from surface and ground waters.  In the broadest sense, travertine includes deposits in both hot and cold springs, including the porous, spongy rock known as tufa,[7][8][4] and also the cave features known as speleothems (which include stalactites and stalagmites).[9][5][7][10][8][4] Calcrete, which is calcium minerals deposited as a horizon in the soil profile, is not considered a form of travertine