Tufa

Tufa is a variety of limestone, formed by the precipitation of carbonate minerals from ambient temperature water bodies. Geothermally heated hot springs sometimes produce similar (but less porous) carbonate deposits known as travertine. Tufa is sometimes referred to as (meteogene) travertine; care must be taken when searching through literature to prevent confusion with hot spring (thermogene) travertine. Calcareous tufa should not be confused with tuff, a porous volcanic rock with parallel etymological origins that is sometimes called "tufa".