The Collaborative International Dictionary
Tufa \Tu"fa\, [It. fufo soft, sandy stone, L. tofus, tophus. Cf. Tofus, Toph, and Tophin.] (Min.)
A soft or porous stone formed by depositions from water, usually calcareous; -- called also calcareous tufa.
A friable volcanic rock or conglomerate, formed of consolidated cinders, or scoria.