![Mono lake tufa](https://upload.wikimedia.org/wikipedia/commons/d/d2/Mono_lake_tufa.JPG)
Tufa is a variety of
limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
formed when
carbonate minerals
Carbonate minerals are those minerals containing the carbonate ion, .
Carbonate divisions Anhydrous carbonates
*Calcite group: trigonal
**Calcite CaCO3
**Gaspéite (Ni,Mg,Fe2+)CO3
**Magnesite MgCO3
**Otavite CdCO3
**Rhodochrosite MnCO3
**Sider ...
precipitate
In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...
out of water in
unheated rivers or lakes.
Geothermally heated hot springs sometimes produce similar (but less porous) carbonate deposits, which are known as
travertine
Travertine ( ) is a form of terrestrial limestone deposited around mineral springs, especially hot springs. It often has a fibrous or concentric appearance and exists in white, tan, cream-colored, and even rusty varieties. It is formed by a p ...
. Tufa is sometimes referred to as (meteogene) travertine.
It should not be confused with hot spring (thermogene) travertine. Tufa, which is
calcareous
Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines.
In zoology
''Calcareous'' is used as an adje ...
, should also not be confused with
tuff
Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock cont ...
, a porous
volcanic rock
Volcanic rock (often shortened to volcanics in scientific contexts) is a rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcanic ...
with a similar
etymology
Etymology ()The New Oxford Dictionary of English (1998) – p. 633 "Etymology /ˌɛtɪˈmɒlədʒi/ the study of the class in words and the way their meanings have changed throughout time". is the study of the history of the Phonological chan ...
that is sometimes also called "tufa".
Classification and features
Modern and fossil tufa deposits abound with wetland plants; as such, many tufa deposits are characterised by their large
macrobiological component, and are highly porous. Tufa forms either in fluvial channels or in lacustrine environments. Ford and Pedley (1996)
provide a review of tufa systems worldwide.
Fluvial deposits
Deposits can be classified by their depositional environment (or otherwise by vegetation or
petrographically
Petrography is a branch of petrology that focuses on detailed descriptions of rocks. Someone who studies petrography is called a petrographer. The mineral content and the textural relationships within the rock are described in detail. The class ...
). Pedley (1990) provides an extensive classification system, which includes the following classes of fluvial tufa:
*Spring – Deposits form on emergence from a
spring/seep. Morphology can vary from
mineratrophic wetlands to spring aprons (see
calcareous sinter
Calcareous sinter is a freshwater calcium carbonate deposit, also known as calc-sinter. Deposits are characterised by low porosity and well-developed lamination, often forming crusts or sedimentary rock layers. Calcareous sinter should not be conf ...
)
*Braided channel – Deposits form within a fluvial channel, dominated by oncoids (see
oncolite
Oncolites are sedimentary structures composed of oncoids, which are layered structures formed by cyanobacterial growth. Oncolites are very similar to stromatolites, but, instead of forming columns, they form approximately spherical structures. T ...
)
*Cascade – Deposits form at waterfalls, deposition is focused here due to accelerated flow (see
Geochemistry
Geochemistry is the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth's crust and its oceans. The realm of geochemistry extends beyond the Earth, encompassing the e ...
)
*Barrage – Deposits form as a series of
phytoherm barrages across a channel, which may grow up to several metres in height. Barrages often contain a significant detrital component, composed of organic material (leaf litter, branches etc.).
Lacustrine deposits
Lacustrine tufas are generally formed at the periphery of lakes and built-up phytoherms (freshwater reefs), and on
stromatolite
Stromatolites () or stromatoliths () are layered sedimentary formations ( microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly proteobacteria). T ...
s.
Oncoids
Oncolites are sedimentary structures composed of oncoids, which are layered structures formed by cyanobacterial growth. Oncolites are very similar to stromatolites, but, instead of forming columns, they form approximately spherical structures. ...
are also common in these environments.
Calcareous sinter
Although sometimes regarded as a distinct carbonate deposit, calcareous sinter formed from ambient temperature water can be considered a sub-type of tufa.
Speleothems
Calcareous
speleothem
A speleothem (; ) is a geological formation by mineral deposits that accumulate over time in natural caves. Speleothems most commonly form in calcareous caves due to carbonate dissolution reactions. They can take a variety of forms, depending on ...
s 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.
Columns
Tufa columns are an unusual form of tufa typically associated with
saline lakes
Saline may refer to:
* Saline (medicine), a liquid with salt content to match the human body
* Saline water, non-medicinal salt water
* Saline, a historical term (especially US) for a salt works or saltern
Places
* Saline, Calvados, a commune ...
. They are distinct from most tufa deposits in that they lack any significant
macrophyte component, due to the salinity excluding
mesophilic organisms.
Some tufa columns may actually form from hot-springs, and may therefore constitute a form of
travertine
Travertine ( ) is a form of terrestrial limestone deposited around mineral springs, especially hot springs. It often has a fibrous or concentric appearance and exists in white, tan, cream-colored, and even rusty varieties. It is formed by a p ...
. It is generally thought that such features form from CaCO
3 precipitated when carbonate rich source waters emerge into alkaline soda lakes. They have also been found in marine settings in the Ikka
fjord
In physical geography, a fjord or fiord () is a long, narrow inlet with steep sides or cliffs, created by a glacier. Fjords exist on the coasts of Alaska, Antarctica, British Columbia, Chile, Denmark, Germany, Greenland, the Faroe Islands, Ice ...
of Greenland where the
Ikaite
Ikaite is the mineral name for the hexahydrate of calcium carbonate, CaCO3·6H2O. Ikaite tends to form very steep or spiky pyramidal crystals, often radially arranged, of varied sizes from thumbnail size aggregates to gigantic salient spurs. It ...
columns can reach up to in height.
Biology
Tufa deposits form an important habitat for a diverse flora.
Bryophyte
The Bryophyta s.l. are a proposed taxonomic division containing three groups of non-vascular land plants (embryophytes): the liverworts, hornworts and mosses. Bryophyta s.s. consists of the mosses only. They are characteristically limited in ...
s (mosses, liverworts etc.) and
diatom
A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...
s are well represented. The porosity of the deposits creates a wet habitat ideal for these plants.
Geochemistry
Modern tufa is formed from alkaline waters, supersaturated with calcite. On emergence, waters degas CO
2 due to the lower atmospheric CO
2 (see
partial pressure
In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas as if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal gas ...
), resulting in an increase in pH. Since carbonate solubility decreases with increased pH, precipitation is induced. Supersaturation may be enhanced by factors leading to a reduction in CO
2, for example increased air-water interactions at waterfalls may be important, as may photosynthesis.
Recently it has been demonstrated that microbially induced precipitation may be more important than physico-chemical precipitation. Pedley et al. (2009) showed with flume experiments that precipitation does not occur unless a
biofilm
A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular ...
is present, despite supersaturation.
Calcite
Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
is the dominant mineral precipitate, followed by the polymorph
aragonite
Aragonite is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, (the other forms being the minerals calcite and vaterite). It is formed by biological and physical processes, including prec ...
.
Occurrence
Tufa is common in many parts of the world, including::
*
Pyramid Lake, Nevada, US – tufa formations
*
Big Soda Lake, Nevada, US – tufa formations only a century old
*
Mono Lake
Mono Lake ( ) is a saline soda lake in Mono County, California, formed at least 760,000 years ago as a terminal lake in an endorheic basin. The lack of an outlet causes high levels of salts to accumulate in the lake which make its water alk ...
, California, US – tufa columns
*
Trona Pinnacles
The Trona Pinnacles are an unusual geological feature in the California Desert National Conservation Area. The landscape consists of more than 500 tufa spires (porous rock formed as a deposit when springs interact with other bodies of water), som ...
, California, US – tufa columns
*
Matlock Bath
Matlock Bath is a village and civil parish in Derbyshire, England. It lies in the Peak District, south of Matlock on the main A6 road, and approximately halfway between Buxton and Derby. The population of the civil parish at the 2011 census wa ...
, Derbyshire, United Kingdom
*
North Dock Tufa, United Kingdom
*
Plitvice Lakes National Park
Plitvice Lakes National Park ( hr, Nacionalni park Plitvička jezera, colloquially ''Plitvice'', ) is one of the oldest and largest national parks in Croatia. In 1979, Plitvice Lakes National Park was inscribed on the UNESCO World Heritage lis ...
, Croatia
*
Basturs Lakes,
Pallars Jussà
Pallars Jussà () is a comarca (county) in Catalonia, Spain. It was established as a ''comarca'' in 1936, out of the old county of Pallars. The name means "Lower Pallars"; to the northeast and into the mountains is Pallars Sobirà. Its capital a ...
,
Catalonia
Catalonia (; ca, Catalunya ; Aranese Occitan: ''Catalonha'' ; es, Cataluña ) is an autonomous community of Spain, designated as a ''nationality'' by its Statute of Autonomy.
Most of the territory (except the Val d'Aran) lies on the north ...
- tufa mounds
*Various parts of Armenia, such as
Artik
Artik (Armenian: ), is a town and urban municipal community in the Shirak Province of Armenia. As of the 2011 census, the town had a population of 19,534. As per the 2016 official estimate, the population of Artik is around 18,800.
Artik is famou ...
*The southwestern coastline of
Western Australia
Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to th ...
*Near
Groot Marico
Groot Marico is a hamlet in the North West Province of South Africa. The economy relies heavily on agriculture, mining and tourism. Groot Marico is named after the Marico River.
Description
The topography comprises dry bushveld with a climate that ...
in the
North West Province
North West is a province of South Africa. Its capital is Mahikeng. The province is located to the west of the major population centre of Gauteng and south of Botswana.
History
North West was incorporated after the end of Apartheid in 1994, an ...
, South Africa
*The
Kadishi Tufa
The Blyde River Canyon is a 26km long Canyon located in Mpumalanga, South Africa. It is the one of the larger canyons on Earth but much smaller than those of Asia, the Grand Canyon and the Fish River Canyon. Unlike the Grand and Fish River Can ...
,
Blyde River Canyon
The Blyde River Canyon is a 26km long Canyon located in Mpumalanga, South Africa. It is the one of the larger canyons on Earth but much smaller than those of Asia, the Grand Canyon and the Fish River Canyon. Unlike the Grand and Fish River Canyon ...
,
Mpumalanga Province, South Africa
Some sources suggest that "tufa" was used as the primary building material for most of the châteaux of the
Loire Valley, France. This results from a mis-translation of the terms "
tuffeau
Tuffeau stone — in French, simply ''tuffeau'' or ''tufeau'' — is a local limestone of the Loire Valley of France. It is characterized as a chalky or sandy, fine-grained limestone, white to yellowish-cream in appearance, and micaceous (cont ...
jaune" and "tuffeau blanc", which are porous varieties of the
Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...
marine limestone known as
chalk
Chalk is a soft, white, porous, sedimentary carbonate rock. It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor. Chalk ...
.
Uses
Tufa is occasionally shaped into a planter. Its porous consistency makes it ideal for
alpine garden
An alpine garden (or alpinarium, alpinum) is a domestic or botanical garden, or more often a part of a larger garden, specializing in the collection and cultivation of alpine plants growing naturally at high altitudes around the world, such as in ...
s. A concrete mixture called
hypertufa
Hypertufa is an anthropic rock made from various aggregates bonded together using Portland cement.
Hypertufa is intended as a manufactured substitute for natural tufa, which is a slowly precipitated limestone rock; being very porous, it is favor ...
is used for similar purposes.
See also
*
References
External links
{{commons+cat
Mono Lake Committee: "Tufa"