TUFA

Tu″fa (?), [[It. fufo soft, sandy stone, L. tofus, tophus. Cf. Tofus, Toph, and Tophin.]] (Min.) (a) A soft or porous stone formed by depositions from water, usually calcareous; — called also calcareous tufa. (b) A friable volcanic rock or conglomerate, formed of consolidated cinders, or scoria.