Tufa is a porous variety of limestone. It is formed by the precipitation of carbonate minerals from water at normal temperatures.
Geothermally heated hot springs sometimes produce similar (but less porous) carbonate deposits known as travertine.
Do not confuse with the rock made of volcanic ash, which is called tuff.
Images for kids
Rubaksa tufa plug, after drying of the river, in Ethiopia
The Pyramid and Domes tufa rock structures, Pyramid Lake, Nevada
Tufa dam in Chelekwot, Ethiopia
In Spanish: Toba calcárea para niños