A soft porous stone, arenaceous, calcareous, or volcanic; esp. a stony substance deposited by calcareous springs.

Any light porous cellular rock; = tufa, n. (But there is a recent tendency to differentiate tuff from… calcareous (or calc) tuff: see tufa, n. a.

‘a porous or vesicular carbonate of lime, generally deposited near the sources and along the courses of calcareous springs’ (Page Handbk. Geol. Terms…

A porous deposit of carbonate of lime, formed by the waters of calcareous springs; calcareous tufa.

Any of several basic or calcareous tuffaceous rocks, usually laminated in structure, affected by low-grade metamorphism; a slaty or sheared…