Source : Webster's Revised Unabridged Dictionary (1913)

Calc-tufa \Calc"-tu`fa\, n. [G. kalk (l. calx) lime + E. tufa.]
   See under {Calcite}.

Source : WordNet®

calc-tufa
     n : a soft porous rock consisting of calcium carbonate deposited
         from springs rich in lime [syn: {tufa}]