Calcareous Tufa

Calcareous Tufa, or CALC-SINTER, consists of carbonate of lime, and is a deposition from springs, streams, or underground water, from which it is precipitated partly by the escape of carbonic acid which acts as a solvent, and partly by evaporation of the water. It is usually white, creamy-white, yellowish, or brownish in colour, but other hues occur, and variegated and mottled varieties are not uncommon. It is of variable texture and consistency; some kinds being rather soft, brittle, and friable, and porous or cellular. These cellular varieties have been deposited from the waters of springs, and often contain vegetable and animal remains, as leaves, twigs, nuts, moss, insects, land and freshwater shells, &c. The so-called 'petrifying springs' of Mortlock afford a good example of the formation of calcareous tufa. In some regions the deposition from calcareous waters is on a very extensive scale, as along the river Arnio, at Tivoli, near Rome, where calcareous tufa occurs in masses many feet in thickness. In that district the formation is harder and more compact, and under the name of travertino is used as a building stone at Rome. Calcareous tufa is abundantly deposited from thermal springs, as in the Yellowstone Region, North America. The calcareous incrustations so commonly seen in caverns in limestone rocks are varieties of calcareous tufa. They are known as Stalactites and Stalagmites (q.v.).