Tufa also callen Sinter is Calcium Carbonate CaCO3 deposit in the form of soft, porous calcite rock. It is usual in water with high concentration of dissolved Calcium Carbonate. However some hard volcanic rocks are also sometimes called Tufa.

Tufa is common in the many parts of the world but most known tufa formations are found on Mono Lake in California. Tufa tower emerged after water flow divert from Mono Lake. Since water evaporation exceed inflow, level of Mono Lake dropped and Tufa Towers emerged. There are many pictures around the net of Tufa Towers and most of them you can find on Flickr.