Tufa

Tufa is a variety of limestone formed when carbonate minerals precipitate out of ambient temperature water. Geothermally heated hot springs sometimes produce similar (but less porous) carbonate deposits known as travertine. Tufa is sometimes referred to as (meteogene) travertine (Allen Pentcost). It should not be confused with hot spring (thermogene) travertine. However, Mono Lake's tufa is thermogene, according to Pentecost. Tufa, which is calcareous, should not be confused with tuff, a porous volcanic rock with a similar etymology that is sometimes also called "tufa".

Modern and fossil tufa deposits abound with wetland plants; as such many tufa deposits are characterised by their large component and are highly porous. Tufa forms either in fluvial channels or in lacustrine settings. Ford and Pedley (1996) provide a review of tufa systems worldwide.

Deposits can be classified by their depositional environment (or otherwise by vegetation or petrographically). Pedley (1990) provides an extensive classification system, which includes the following classes of fluvial tufa:

Lacustrine tufas are generally formed at the periphery of lakes and build up phytoherms (freshwater reefs) and stromatolites. Oncoids are also common in these environments.

While fluvial and lacustrine systems make up the bulk of tufa systems worldwide, there are several other important tufa environments.

Although sometimes regarded as a distinct carbonate deposit, calcareous sinter formed from ambient temperature water can be considered a sub-type of tufa.

Calcareous speleothems may be regarded as a form of calcareous sinter. They lack any significant macrophyte component due to the absence of light, and for this reason they are often morphologically closer to travertine or calcareous sinter.

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