Flowstones are sheetlike deposits of

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 ...

or other carbonate minerals, formed where water flows down the walls or along the floors of a

cave Caves or caverns are natural voids under the Earth's Planetary surface, surface. Caves often form by the weathering of rock and often extend deep underground. Exogene caves are smaller openings that extend a relatively short distance undergrou ...

. They are typically found in "solution caves", in

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

, where they are the most common

speleothem A speleothem (; ) is a geological formation made 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, depen ...

. 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 The vadose zone (from the Latin word for "shallow"), also termed the unsaturated zone, is the part of Earth between the land surface and the top of the phreatic zone, the position at which the groundwater (the water in the soil's pores) is at ...

percolation waters. 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 Calthemite is a secondary deposit, derived from concrete, Lime (material), lime, Mortar (masonry), mortar or other calcareous material outside the cave environment.Smith, G.K. (2016). "Calcite straw stalactites growing from concrete structures" ...

s" and are associated with

concrete degradation Concrete degradation may have many different causes. Concrete is mostly damaged by the corrosion of reinforcement bars, the carbonatation of hardened cement paste or chloride attack under wet conditions. Chemical damage is caused by the formati ...

.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.

Formation

Flowing films of water that move along floors or down positive-sloping walls build up layers of

calcium carbonate Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...

(calcite),

aragonite Aragonite is a carbonate mineral and one of the three most common naturally occurring crystal forms of calcium carbonate (), the others being calcite and vaterite. It is formed by biological and physical processes, including precipitation fr ...

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate Hydrate, dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, drywall and blackboard or sidewalk ...

, or other cave

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...

s. These minerals are dissolved in the water and are deposited when the water loses its dissolved

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

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 Tufa is a variety of limestone formed when carbonate minerals precipitation (chemistry), precipitate out of water in ambient temperature, unheated rivers or lakes. hot spring, Geothermally heated hot springs sometimes produce similar (but less ...

and

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 rusty varieties. It is formed by a process ...

. 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 A stalagmite (, ; ; ) is a type of rock formation that rises from the floor of a cave due to the accumulation of material deposited on the floor from ceiling drippings. Stalagmites are typically composed of calcium carbonate, but may consist ...

s and

stalactite A stalactite (, ; , ) is a mineral formation that hangs from the ceiling of caves, hot springs, or man-made structures such as bridges and mines. Any material that is soluble and that can be deposited as a colloid, or is in suspension (chemistry ...

s. The deposits may grade into thin sheets called "

draperies Drapery is a general word referring to cloths or textiles (Old French , from Late Latin">-4; we might wonder whether there's a point at which it's appropriate to talk of the beginnings of French, that is, when it wa ... , from Late Latin ). It ma ...

" 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 Bacon is a type of Curing (food preservation), salt-cured pork made from various cuts of meat, cuts, typically the pork belly, belly or less fatty parts of the back. It is eaten as a side dish (particularly in breakfasts), used as a central in ...

(often termed "cave bacon"). Though flowstones are among the largest of

s, they can still be damaged by a single touch. The 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.

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.Hill, C A, and Forti, P, (1997). Cave Minerals of the World, (2nd edition). untsville, Alabama: National Speleological Society Inc.pp. 217 and 225 On concrete structures, these secondary deposits are the result of

,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 when calcium ions have been leached from the concrete in solution and redeposited on the structure's surface to form flowstone, stalactites and stalagmites.

Carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

(CO₂) is absorbed into the hyperalkaline leachate solution as it emerges from the concrete. This facilitates the chemical reactions which deposits

(CaCO₃) on vertical or sloping surfaces, in the form of flowstone. Concrete derived secondary deposits are classified as "

s". These calcium carbonate deposits mimic the forms and shapes of

s, created in caves. e.g.

s, flowstone etc. It is most likely that calthemite flowstone is precipitated from leachate solution as

, "in preference to the other, less stable polymorphs,

and

vaterite Vaterite is a mineral, a polymorphism (materials science), polymorph of calcium carbonate (calcium, Cacarbon, Coxygen, O3). It was named after the German mineralogist Heinrich Vater. It is also known as mu-calcium carbonate (μ-CaCO3). Vaterite b ...

." 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 CaCO₃. This may cause the calthemites to take on colours of the leached oxides.White W.B., (1997), “Color of Speleothems”, Cave Minerals of the World, (2nd Edition) Hill C. and Forti P. untsville, Alabama: National Speleological Society Inc.239-244

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 Tennessee (, ), officially the State of Tennessee, is a landlocked U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders Kentucky to the north, Virginia to the northeast, North Carolina t ...

Alabama Alabama ( ) is a U.S. state, state in the Southeastern United States, Southeastern and Deep South, Deep Southern regions of the United States. It borders Tennessee to the north, Georgia (U.S. state), Georgia to the east, Florida and the Gu ...

Georgia Georgia most commonly refers to: * Georgia (country), a country in the South Caucasus * Georgia (U.S. state), a state in the southeastern United States Georgia may also refer to: People and fictional characters * Georgia (name), a list of pe ...

area and the

Ozarks The Ozarks, also known as the Ozark Mountains, Ozark Highlands or Ozark Plateau, is a physiographic region in the U.S. states of Missouri, Arkansas, and Oklahoma, as well as a small area in the southeastern corner of Kansas. The Ozarks cover ...

—during the 19th and early 20th centuries, being applied to calcite speleothems that were banded in a way suggestive of true

onyx Onyx is a typically black-and-white banded variety of agate, a silicate mineral. The bands can also be monochromatic with alternating light and dark bands. ''Sardonyx'' is a variety with red to brown bands alternated with black or white bands. ...

. There are a number of US caves called " Onyx Cave" because of the presence in them of such deposits.

Gallery

File:MysteryCaveFlowstone.jpg, Flowstone in Mystery Cave,

Minnesota Minnesota ( ) is a U.S. state, state in the Upper Midwestern region of the United States. It is bordered by the Canadian provinces of Manitoba and Ontario to the north and east and by the U.S. states of Wisconsin to the east, Iowa to the so ...

File:Gunns caves flowstone.JPG, Flowstone on the ceiling at Gunns Plains Cave,

Tasmania Tasmania (; palawa kani: ''Lutruwita'') is an island States and territories of Australia, state of Australia. It is located to the south of the Mainland Australia, Australian mainland, and is separated from it by the Bass Strait. The sta ...

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 CaCO₃. A sign of concrete degradation. File:Calthemite flowstone with Iron Oxide deposited along with CaCO3.jpg, Calthemite flowstone on concrete wall.

References

External links

The Virtual Cave: Flowstone
{{Caves Speleothems