Editing Travertine (section)

==Definition==
Travertine is a [[sedimentary rock]] formed by the [[precipitation (chemistry)|chemical precipitation]] of [[calcium carbonate]] [[mineral]]s from fresh water,<ref name=AllabyTravertine>{{cite book |last1=Allaby |first1=Michael |title=A dictionary of geology and earth sciences |date=2013 |publisher=Oxford University Press |location=Oxford |isbn=9780199653065 |edition=Fourth |chapter=travertine}}</ref> typically in springs, rivers, and lakes;<ref name=BMM>{{cite book |last1=Blatt |first1=Harvey |last2=Middleton |first2=Gerard |last3=Murray |first3=Raymond |title=Origin of sedimentary rocks |date=1980 |publisher=Prentice-Hall |location=Englewood Cliffs, N.J. |isbn=0136427103 |edition=2d |pages=479–480}}</ref><ref name=leeder>{{cite book |last1=Leeder |first1=M. R. |title=Sedimentology and sedimentary basins : from turbulence to tectonics |date=2011 |publisher=Wiley-Blackwell |location=Chichester, West Sussex, UK |isbn=9781405177832 |edition=2nd |page=42}}</ref> that is, from surface and ground waters.{{sfn|Jackson|1997|loc="travertine"}} In the broadest sense, travertine includes deposits in both hot and cold springs, including the porous, spongy rock known as [[tufa]],{{sfn|Jackson|1997|loc="travertine"}}<ref name=KK/><ref name=AllabyTravertine/> and also the [[cave]] features known as [[speleothem]]s (which include [[stalactite]]s and [[stalagmite]]s).<ref>{{cite book |last1=Thornbury |first1=William D. |title=Principles of geomorphology |date=1969 |publisher=Wiley |location=New York |isbn=0471861979 |pages=325–327 |edition=2d}}</ref><ref name=BMM/>{{sfn|Jackson|1997|loc="travertine"}}<ref name=Pentecost>{{cite book |last1=Pentecost |first1=Allan |title=Travertine |date=2005 |publisher=Springer |isbn=9781402035234 |page=4}}</ref><ref name=KK>{{cite book |last1=Lillie |first1=Robert J. |title=Parks and plates : the geology of our national parks, monuments, and seashores |date=2005 |publisher=W.W. Norton |location=New York |isbn=0393924076 |edition=1st}}</ref><ref name=AllabyTravertine/> [[Caliche|Calcrete]], which is calcium minerals deposited as a horizon in the [[soil profile]], is not considered a form of travertine.{{sfn|Jackson|1997|loc="travertine"}}{{sfn|Pentecost|2005|p=4}}
[[File:Kalktuff-Mosscrusts.jpg|thumb|upright|Calcium-carbonate-encrusted, growing moss in a low-temperature freshwater travertine formation (1 [[euro]] coin for scale)]]

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.<ref name=BMM/>{{sfn|Jackson|1997|loc="travertine"}}<ref name=AllabyTravertine/><ref name=leeder/> In this more narrow sense, travertine is distinct from speleothems<ref>{{cite book |last1=Klein |first1=Cornelis |last2=Hurlbut |first2=Cornelius S. Jr. |title=Manual of mineralogy : (after James D. Dana) |date=1993 |publisher=Wiley |location=New York |isbn=047157452X |edition=21st |page=407}}</ref> and [[tufa]].<ref name=BMM/>{{sfn|Ford|Pedley|1996}}<ref name=leeder/> 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, lake [[marl]]s, and lake reefs are excluded from this definition, but both speleothems and [[tufa]] are included.{{sfn|Pentecost|2005|pp=3–4}}

Fresh travertines vary widely in their [[porosity]], from about 10% to 70%. Ancient ones may have porosities as low as 2% due to [[crystallization]] of secondary calcite in the original pore spaces, while some of the fresh [[aragonite]] travertine at [[Mammoth Hot Springs]] in 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%.{{sfn|Pentecost|2005|pp=30–31}}