Editing Flowstone

{{Short description|Geological phenomenon}}
{{more footnotes|date=December 2013}}
[[File:Saracen's Tent, Luray Caverns.jpg|thumb|''Saracen's tent'' in [[Luray Caverns]] in [[Virginia]] is considered to be one of the most well-formed flowstone draperies in the world]]

'''Flowstones''' are sheetlike deposits of [[calcite]] or other carbonate minerals, formed where water flows down the walls or along the floors of a [[cave]].<ref>Hill, C A, and Forti, P, (1997). Cave Minerals of the World,  (2nd edition). [Huntsville, Alabama: National Speleological Society Inc.] p.70</ref> They are typically found in "solution caves", in [[limestone]], where they are the most common [[speleothem]]. However, they may form in any type of cave where water enters that has picked up dissolved minerals. Flowstones are formed via the degassing of [[vadose]] percolation waters.<ref name=Drysdale>{{cite journal |doi=10.1130/G22103.1 |title=Late Holocene drought responsible for the collapse of Old World civilizations is recorded in an Italian cave flowstone |year=2006 |last1=Drysdale |first1=Russell |last2=Zanchetta |first2=Giovanni |last3=Hellstrom |first3=John |last4=Maas |first4=Roland |last5=Fallick |first5=Anthony |last6=Pickett |first6=Matthew |last7=Cartwright |first7=Ian |last8=Piccini |first8=Leonardo |journal=Geology |volume=34 |issue=2 |pages=101|bibcode=2006Geo....34..101D }}</ref>

Flowstone may also form on manmade structures as a result of calcium hydroxide being leached from  concrete, lime or mortar. These secondary deposits created outside the cave environment, which mimic the shapes and forms of speleothems, are classified as "[[calthemite]]s" and are associated with [[concrete degradation]].<ref name=smith2016>Smith, G.K., (2016). “Calcite Straw Stalactites Growing From Concrete Structures”, Cave and Karst Science, Vol.43, No.1, P.4-10, (April 2016), British Cave Research Association, ISSN 1356-191X.</ref>

==Formation==
[[File:Tropfsteine.svg|right|thumb|Diagram of dripstone cave structures (flowstone labelled AB)]]
Flowing films of water that move along floors or down positive-sloping walls build up layers of [[calcium carbonate]] (calcite), [[aragonite]], [[gypsum]],<ref>Hill, C A, and Forti, P, (1997). Cave Minerals of the World,  (2nd edition). [Huntsville, Alabama: National Speleological Society Inc.] pp 193 and 196</ref><ref>Szablyár, P., (1981) “Morphogenetics of Umm al Massabih Cave (Libya)”, Karszt és Barlang, No. 1, P27-34. In Hungarian.</ref> or other cave [[mineral]]s. These minerals are dissolved in the water and are deposited when the water loses its dissolved [[carbon dioxide]] through the mechanism of agitation, meaning it can no longer hold the minerals in solution. The flowstone forms when thin layers of these deposits build on each other, sometimes developing more rounded shapes as the deposit gets thicker.

There are two common forms of flowstones, [[tufa]] and [[travertine]].  Tufa is usually formed via the precipitation of calcium carbonate, and is spongy or porous in nature.  Travertine is a calcium carbonate deposit often formed in creeks or rivers; its nature is laminated, and it includes such structures as [[stalagmite]]s and [[stalactite]]s.

The deposits may grade into thin sheets called "[[drapery (geology)|draperies]]" or "curtains" where they descend from overhanging portions of the wall. Some draperies are translucent, and some have brown and beige layers that look much like [[bacon]] (often termed "cave bacon").

Though flowstones are among the largest of [[speleothem]]s, they can still be damaged by a single touch. The [[sebum|oil from human fingers]] causes the flowing water to avoid the area, which then dries out.  Flowstones are also good identifiers of periods of past droughts, since they need some form of water to develop; the lack of that water for long periods of time can leave traces in the rock record via the absence or presence of flowstones, and their detailed structure.<ref name=Drysdale/>

===Concrete derived flowstone===
Flowstone derived from concrete, lime or mortar, can form on manmade structures, much more rapidly than in the natural cave environment due to the different chemistry involved.<ref name=Hill&Forti1997>Hill, C A, and Forti, P, (1997). Cave Minerals of the World,  (2nd edition). [Huntsville, Alabama: National Speleological Society Inc.] pp. 217 and 225</ref>
On concrete structures, these secondary deposits are the result of [[concrete degradation]],<ref>Macleod, G, Hall, A J and Fallick, A E, (1990). "An applied mineralogical investigation of concrete degradation in a major concrete road bridge". Mineralogical Magazine, Vol.54, 637–644</ref><ref name=SmithGK2016>Smith G.K., (2016). "Calcite straw stalactites growing from concrete structures", Cave and Karst Science, Vol.43, No.1, P.4-10, (April 2016), British Cave Research Association, ISSN 1356-191X</ref> when calcium ions have been leached from the concrete in solution and redeposited on the structure's surface to form flowstone, stalactites and stalagmites.<ref name=Hill&Forti1997 /> [[Carbon dioxide]] (CO<sub>2</sub>) is absorbed into the hyperalkaline leachate solution as it emerges from the concrete. This facilitates the chemical reactions which deposits [[calcium carbonate]] (CaCO<sub>3</sub>) on vertical or sloping surfaces, in the form of flowstone.<ref name=Hill&Forti1997 /><ref name=SmithGK2016 />

Concrete derived secondary deposits are classified as "[[calthemite]]s".<ref name=SmithGK2016 /> These calcium carbonate deposits mimic the forms and shapes of [[speleothem]]s, created in caves. e.g. [[stalagmite]]s, [[stalactite]]s, flowstone etc. It is most likely that calthemite flowstone is precipitated from leachate solution as [[calcite]], "in preference to the other, less stable [[polymorphism (materials science)|polymorphs]], [[aragonite]] and [[vaterite]]."<ref name=SmithGK2016 />

Other trace elements such as iron from rusting reinforcing or copper oxide from pipework may be transported by the leachate and deposited at the same time as the CaCO<sub>3</sub>.<ref name=SmithGK2016 /> This may cause the calthemites to take on colours of the leached oxides.<ref>White W.B., (1997), “Color of Speleothems”, Cave Minerals of the World, (2nd Edition) Hill C. and Forti P. [Huntsville, Alabama: National Speleological Society Inc.] 239-244</ref><ref name=SmithGK2016 />

==Uses==
'''Cave onyx''' is any of various kinds of flowstone considered desirable for ornamental architectural purposes. "Cave onyx" was a common term in certain areas of the United States—particularly the [[Tennessee]]-[[Alabama]]-[[Georgia (U.S. state)|Georgia]] area and the [[Ozarks]]—during the 19th and early 20th centuries, being applied to calcite speleothems that were banded in a way suggestive of true [[onyx]].

There are a number of US caves called "[[Onyx Cave (disambiguation)|Onyx Cave]]" because of the presence in them of such deposits.

== Gallery ==
<gallery mode=packed>
File:MysteryCaveFlowstone.jpg|Flowstone in [[Mystery Cave]], [[Minnesota]]
File:Gunns caves flowstone.JPG|Flowstone on the ceiling at [[Gunns Plains Cave]], [[Tasmania]]
File:Flowstone in Mammoth Cave, KY.jpg|Travertine flowstone formation in Mammoth Cave, KY, USA
File:Calthemite flowstone on concrete - Iron Stained.jpg|Calthemite flowstone on concrete wall, colored by iron oxide deposited with the [[Calcium carbonate|CaCO<sub>3</sub>]]. A sign of concrete degradation.
File:Calthemite flowstone with Iron Oxide deposited along with CaCO3.jpg|Calthemite flowstone on concrete wall.
</gallery>

== References ==
{{Reflist}}

== External links ==
{{commons category|Flowstones}}
* [http://www.goodearthgraphics.com/virtcave/flowstone/flowstone.html The Virtual Cave: Flowstone]

{{Caves}}

[[Category:Speleothems]]