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Travertine

From Wikipedia, the free encyclopedia

Travertine terraces atMammoth Hot Springs,Yellowstone National Park,in 2016
Calcium-carbonate-encrusted, growing moss in a low-temperature freshwater travertine formation (1eurocoin for scale)

Travertine(/ˈtrævərtn/TRAV-ər-teen)[1]is a form of terrestriallimestonedeposited aroundmineral springs,especiallyhot springs.It often has a fibrous or concentric appearance and exists in white, tan, cream-colored, and rusty varieties.[2][3]It is formed by a process of rapid precipitation ofcalcium carbonate,often at the mouth of a hot spring or in a limestone cave. In the latter, it can formstalactites,stalagmites,and otherspeleothems.It is frequently used in Italy and elsewhere as abuilding material.Similar (but softer and extremely porous) deposits formed from ambient-temperature water are known astufa.

Definition

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Travertine is asedimentary rockformed by thechemical precipitationofcalcium carbonatemineralsfrom fresh water,[4]typically in springs, rivers, and lakes;[5][6]that is, from surface and ground waters.[7]In the broadest sense, travertine includes deposits in both hot and cold springs, including the porous, spongy rock known astufa,[7][8][4]and also thecavefeatures known asspeleothems(which includestalactitesandstalagmites).[9][5][7][10][8][4]Calcrete,which is calcium minerals deposited as a horizon in thesoil profile,is not considered a form of travertine.[7][11]

Travertine is often defined in a more narrow sense as dense rock, sometimes massive but more commonly banded or with a fibrous internal structure, deposited in hot springs.[5][7][4][6]In this more narrow sense, travertine is distinct from speleothems[12]andtufa.[5][13][6]Travertine is sometimes defined by its mode of origin, as rock formed by inorganic precipitation of calcium carbonate minerals onto a surface following exchange of carbon dioxide between the atmosphere and groundwater. Calcrete, lakemarls,and lake reefs are excluded from this definition, but both speleothems andtufaare included.[14]

Fresh travertines vary widely in theirporosity,from about 10% to 70%. Ancient ones may have porosities as low as 2% due tocrystallizationof secondary calcite in the original pore spaces, while some of the fresharagonitetravertine atMammoth Hot Springsin Wyoming has a porosity greater than 80%. A porosity of about 50% is typical for cold spring travertine while hot spring travertines have a mean porosity of about 26%. Speleothems have low porosities of less than 15%.[15]

Landforms

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Travertine forms distinctive landforms:

  • Spring mounds are domes of travertine ranging in height from less than a meter to over 100 metres (330 ft) surrounding a spring orifice. Because the spring orifice is above ground level, the formation of terrestrial mounds requires either anartesianspring or ageyser.Travertine mounds also are found under water, often in saline lakes.[16]
  • Fissure ridges form from spring discharge alongjointsorfaults.These can be over 15 metres (49 ft) in height and 0.5 kilometres (0.31 mi) in length. These generally show signs of progressive widening of the fissure, balanced bydepositionof travertine on the fissure wall.[17]
  • Cascade deposits are formed by a series of waterfalls.[18]
  • Dam deposits are similar to cascades but have localized vertical buildup of travertine that creates a pond or lake behind the travertine buildup.[19]
  • Travertine forms various kinds offluvialandlacustrine deposits.[20]
  • Paludal (marsh) deposits are shallow accumulations in poorly-drained areas.[21]
  • Speleothems are the characteristic "formations" of caves.[22]

Etymology

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The word 'travertine' is derived from the Italiantravertino,a derivation of the Latintiburtinusmeaning 'of Tibur', now known asTivoli,near Rome, Italy.[23][24]

Geochemistry

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The formation of travertine begins whengroundwater(H2O) containing an elevated concentration of dissolvedcarbon dioxide(CO2) comes in contact withlimestoneor other rock containing calcium carbonate (CaCO3). The dissolved carbon dioxide acts as a weak acid,carbonic acid,which dissolves some of the limestone as solublecalcium bicarbonate(Ca+2+ 2HCO3):

CaCO3+ H2O + CO2⇌ Ca2++ 2HCO3

This is areversible reaction,meaning that as the concentration of dissolved calcium bicarbonate builds up, the calcium bicarbonate begins to revert tocalcium carbonate,water, and carbon dioxide. So long as there is nowhere for the carbon dioxide to go,chemical equilibriumis reached where dissolution of calcium carbonate is balanced by precipitation of calcium carbonate.[25]

If the groundwater moves into an environment with a lower concentration of carbon dioxide (as measured by itspartial pressure,pCO2), some of the carbon dioxide will escape into the environment, disturbing the equilibrium and allowing net precipitation of calcium carbonate to take place:

Ca2++ 2HCO3→ CaCO3+ H2O + CO2

The calcium carbonate most readily precipitates onto solid surfaces bathed by the groundwater, eventually building up thick deposits of travertine. Because of the role of CO2in dissolving and transporting calcium carbonate, it is sometimes described as thecarrier CO2or simply as thecarrier.[25]

The most important sources of elevated carbon dioxide concentration in groundwater are soil and volcanic activity. Water passing through soil picks up carbon dioxide from plant roots and decayingorganic matter.[26]This CO2is described asmeteoric carrier,and the travertine formed by this mechanism asmeteogene travertine.[25]This is the principal mechanism for formation of speleothems. Groundwater with an enhanced concentration of CO2absorbed from soil infiltrates underlying limestone, dissolving some of the limestone. When this groundwater then emerges into a cave with a lower concentration of CO2,some of the CO2escapes, allowing calcium carbonate to precipitate and build up stalactites, stalagmites, and other speleothems.[27][28]

Volcanic activity is the source of carbon dioxide in groundwater that emerges from hot springs. When the water reaches the mouth of the spring, it rapidly loses carbon dioxide to the open air and precipitates calcium carbonate around the spring mouth. Travertine formed this way is described asthermogene travertine.[25]This can form spectacular deposits of travertine, such as those ofPamukkaleor Mammoth Hot Springs. The carbon dioxide may come from sources deep in the Earth,[29][30]such asmetamorphismof deeply buried rock. The carbon dioxide is carried to the surface bymagmaand is a major component ofvolcanic gases.[31][32]Carbon dioxide may also be generated by magma bodies heating solid rock near the surface, through thermal decomposition of organic matter, or by reactions ofquartzor othersilicaminerals withcarbonate minerals.[33]

Precipitationmay be enhanced by factors leading to a reduction in pCO2,for example increased air-water interactions at waterfalls may be important,[34]as may photosynthesis.[35]

Rarely, travertine may form from highlyalkalinewater containing dissolvedcalcium hydroxide(Ca+2+ 2OH) produced duringserpentinizationofultramaficrock. When this alkaline water reaches the surface, it absorbs carbon dioxide from the air to precipitate calcium carbonate:[25]

Ca2++ 2OH+ CO2→ CaCO3+ H2O

While water carbonated by volcanic activity is usually associated with hot springs, such water occasionally cools to near ambient temperature before emerging at the surface. Likewise, water carbonated by passage through soil will occasionally have circulated to sufficient depths that it is quite warm when it reemerges at the surface. Water carbonated by volcanic activity will nonetheless tend to have a higher content of dissolved calcium bicarbonate and will generally be more enriched in the heavier13C isotope.[36]

Both of the major calcium carbonate minerals,calciteandaragonite,are found in hot spring travertines; aragonite is preferentially precipitated when temperatures are high, while calcite dominates when temperatures are lower.[37][38]When pure and fine, travertine is white, but often it is brown to yellow due to impurities.

Occurrence

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Travertine is found in hundreds of locations around the world.[39]Only a sampling of notable occurrences is listed here.

Badab-e Surt's stepped travertine terrace formations. This travertine owes its red colourterracestoiron carbonate.
Mausoleumsubmerged in a travertine pool atHierapolishot springs, Turkey

Travertine is found at Tivoli, 25 kilometers (16 mi) east of Rome, where the travertine has been quarried for at least 2,000 years.[40]Tivoli travertine was deposited in a body 20 square kilometers (7.7 sq mi) in area and 60 meters (200 ft) thick along a north-trending fault near the dormantColli Albanivolcano. The Guidonia quarry is located in this deposit of travertine.[41]The ancient name for this stone waslapis tiburtinus,meaningtibur stone,which was gradually corrupted totravertino(travertine). Detailed studies of the Tivoli andGuidoniatravertine deposits revealed diurnal and annual rhythmic banding and laminae, which have potential use ingeochronology.[42]Deposits of travertine are found in about 100 other locations in Italy, including Rapalino nearPisa.

Cascades of natural lakes formed behind travertine dams can be seen inPamukkale,Turkey, which is aUNESCO World Heritage Site.Other places with such cascades includeHuanglonginSichuanProvince of China (another UNESCO World Heritage Site), the Mammoth Hot Springs in the United States,Egerszalókin Hungary,Mahallat,Abbass Abad, Atash Kooh, andBadab-e SurtinIran,Band-i-AmirinAfghanistan,Lagunas de Ruidera,Spain,Hierve el Agua,Oaxaca, MexicoandSemuc Champey,Guatemala.

InCentral Europe's last post-glacial palaeoclimatic optimum (Atlantic Period,8000–5000 BC), huge deposits oftufaformed fromkarst springs.On a smaller scale, these karst processes are still working.[43]Importantgeotopesare found at theSwabian Alb,mainly in valleys at the foremost northwest ridge of thecuesta;[44][45]in many valleys of the eroded periphery of the karsticFranconian Jura;and at the northernAlpine foothills.[46][47]

Dinaric karstwatercourses, especially those in Bosnia and Herzegovina and Croatia, are known for build-up of rich travertine deposits and associated phenomena such as tufa and travertine caves, river islets, barriers and waterfalls.[48][49]In Bosnia and HerzegovinaUna riveris particularly rich in deposits,[50]and so isPliva,Trebižat,Buna,Bregava.[48]Travertine has formed 16 natural dams in a valley inCroatiaknown asPlitvice Lakes National Park.Clinging to moss and rocks in the water, the travertine has built up over several millennia to form waterfalls up to 70 m (230 ft) in height.[51][49]Also in Croatia theKrka,Zrmanjawith Krupa tributary, andKupain Croatia and Slovenia, andKrkain Slovenia.

Tufa and travertine sediments visible on the Una river bed.
Tufa and travertine deposits on Plitvice waterfalls

In the United States, the most well-known place for travertine formation isYellowstone National Park,where thegeothermal areasare rich in travertine deposits.[52]Wyoming also has travertines inHot Springs State ParkinThermopolis.[53]Oklahomahas two parks dedicated to this natural wonder.Turner Falls,the tallest waterfall in Oklahoma, is a 77 feet (23 m) cascade of spring water flowing over a travertine cave. Honey Creek feeds this waterfall and creates miles of travertine shelves both up and downstream. Many small waterfalls upstream in the dense woods repeat the travertine-formation effect.[54]Another travertine resource is inSulphur, Oklahoma,10 miles (16 km) east of Turner Falls. Travertine Creek flows through a spring-water nature preserve within the boundaries of theChickasaw National Recreation Area.[55]

Austin, Texas,and the surrounding "Hill Country" to the south is built on limestone. The area has many travertine formations, such as those found at Gorman Falls withinColorado Bend State Park.[56]Hanging LakeinGlenwood Canyonin Colorado was formed by travertine dams across a spring-fed stream.[57]Travertine beds in the area are as much as 40 feet (12 m) thick.[58]Rifle Falls State Parkin Colorado features a triple waterfall over a travertine dam.[59][60]

Soda Dam, Jemez Mountains, New Mexico

TheSoda Dam Hot Springsystem of theJemez Mountainsof New Mexico have been intensively investigated because of its connection to the geothermal system of theValles caldera.Hot groundwater from the caldera has moved along the Jemez fault, and mixed with cooler groundwater before emerging at the surface.Radiometric datingof the travertines show that deposition began almost immediately after the Valles caldera eruption and that the area is experiencing deposition that began 5,000 years ago.[61]A new species of theextremophilegreen algaeScenedesmuswas first isolated from the travertine of Soda Dam.[62]

InIceland,the Hvanná river, located at the north flank of theEyjafjallajökull,was heavily charged with CO2following the2010 eruptions.Travertine precipitated along the river.[63]

Uses

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Sacré-Cœur, Paris,(1875–1914)

Travertine is often used as abuilding material.It typically lacks planes of weakness, and its high porosity makes it light in weight for its strength, gives it good thermal and acoustic insulating properties, and makes it relatively easy to work. Dense travertine makes excellent decorative stone when polished.[64]

TheRomans mineddeposits of travertine for building temples, monuments,[65]aqueducts,[66]bath complexes,[67]and amphitheaters such as theColosseum,[68]the largest building in the world constructed mostly of travertine.[69]In Italy, well-known travertine quarries exist in Tivoli and Guidonia Montecelio, where the most important quarries since Ancient Roman times can be found.[70]The Tivoli quarries supplied the travertine from whichGian Lorenzo Berniniselected material from which to build the colonnade ofSt. Peter's Squarein Rome (colonnato di Piazza S. Pietro) in 1656–1667.[71]Michelangeloalso chose travertine as the material for the external ribs of the dome ofSt. Peter's Basilica.[72]Travertine from Tivoli was used in the sculpting of the majority of theTrevi Fountainin Rome during theBaroqueperiod.[73]

Travertine regained popularity as a building material in the Middle Ages.[74]The central German town ofBad Langensalzahas an extant medieval old town built almost entirely of local travertine.[citation needed]Twentieth century buildings using travertine extensively include theSacré-Cœur BasilicainParis,theGetty CenterinLos Angeles,California, andShell-HausinBerlin.The travertine used in the Getty Center and Shell-Haus constructions was imported from Tivoli and Guidonia.[75]

Travertine is one of several natural stones that is used for paving patios and garden paths.[76]It is sometimes known as travertine limestone or travertine marble; these are the same stone, although travertine is classified properly as a type of limestone, notmarble.The stone is characterised by pitted holes and troughs in its surface. Although these troughs occur naturally, they suggest signs of considerable wear and tear over time. It can be polished to a smooth, shiny finish, and comes in a variety of colors from grey to coral-red. Travertine is available intilesizes for floor installations.[77][78]

Travertine is one of the most frequently used stones inmodern architecture.It is commonly used for indoor home/business flooring, outdoor patio flooring, spa walls and ceilings, façades, and wallcladding.The lobby walls of themodernistWillis Tower(1970) (formerly Sears Tower) inChicagoare made of travertine.[79]ArchitectWelton Becketfrequently incorporated travertine into many of his projects.[80]TheRonald Reagan UCLA Medical Centeris clad with over 3 million pounds (about 1360 tonnes) of Ambra Light travertine from the Tivoli quarries.[81]ArchitectLudwig Mies van der Roheused travertine in several of his major works, including theToronto-Dominion Centre,[82]S.R. Crown Hall,[83]theFarnsworth House[84]and theBarcelona Pavilion.[85]TheNew Mexico State Capitolhas its rotunda finished with travertine[86]mined from a deposit west ofBelen, New Mexico.Stone from this quarry is also used in buildings at theUniversity of New Mexico.[87][88]

Supply

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Until the 1980s, Italy had a near-monopoly on the world travertine market; now significant supplies are quarried in Turkey, Mexico,China,Peru,and Spain. US imports of travertine in 2019 were 17,808 metric tons, of which 12,804 were from Turkey.[89]

See also

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  • Alabaster– Lightly colored, translucent, and soft calcium minerals, typically gypsum – see the variety called "onyx-marble", actually a travertine
  • Calcareous sinter– Freshwater calcium carbonate deposit
  • Calthemite– Secondary calcium carbonate deposit growing under man-made structures
  • Karst topography– Topography from dissolved soluble rocks
  • List of types of limestone– Limestone deposits listed by location

References

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