Flowstones are composed of sheetlike deposits of calcite or other carbonate minerals, formed where water flows down the walls or along the floors of a cave. They are found in "solution caves", in limestone, where they are the most common speleothem. However, they may form in any type of cave. Flowstones are formed via the degassing of vadose percolation waters. Flowstone may 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 "calthemites" and are associated with concrete degradation. Flowing films of water that move along floors or down positive-sloping walls build up layers of calcium carbonate, gypsum, or other cave minerals; 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 and travertine. Tufa is formed via the precipitation of calcium carbonate, is spongy or porous in nature. Travertine is a calcium carbonate deposit formed in creeks or rivers; the deposits may grade into thin sheets called "draperies" or "curtains" where they descend from overhanging portions of the wall. Some draperies are translucent, some have brown and beige layers that look much like bacon. Though flowstones are among the largest of speleothems, they can still be damaged by a single touch; the oil from human fingers causes the flowing water to avoid the area, which dries out. Flowstones are good identifiers of periods of past droughts, since they need some form of water to develop. Flowstone derived from concrete, lime or mortar, can form on manmade structures, much more than in the natural cave environment due to the different chemistry involved.
On concrete structures, these secondary deposits are the result of concrete degradation, when calcium ions have been leached from the concrete in solution and redeposited on the structure's surface to form flowstone and stalagmites. Carbon dioxide is absorbed into the hyperalkaline leachate solution; this facilitates the chemical reactions which deposits calcium carbonate on vertical or sloping surfaces, in the form of flowstone. Concrete derived secondary deposits are classified as "calthemites"; these calcium carbonate deposits mimic the shapes of speleothems, created in caves. E.g. stalagmites, flowstone etc. It is most that calthemite flowstone is precipitated from leachate solution as calcite, "in preference to the other, less stable polymorphs and vaterite." 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.
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 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" because of the presence in them of such deposits; the Virtual Cave: Flowstone
Ogof y Daren Cilau
Ogof y Daren Cilau is one of several cave systems in the Llangattock escarpment near Crickhowell in south Powys, Wales. The cave is one of the longest cave systems in the country, it is one of the longest systems in the country and the entrance section is long and strenuous, making the trip into the further parts of the cave a serious undertaking. Its awkward 517 m entrance crawl is a natural barrier to any casual visitor and precludes the need for a locked gate to protect it from vandals. Highlights of Daren Cilau include the largest cave passage in Britain. Due to the extent of the passages several kilometres from the entrance which would require trips of up to 20 hours to explore, some permanent underground camps have been established including the Restaurant at the End of the Universe, some thirteen hours from the entrance; the entrance to the cave was discovered in 1957 by Vic Howells. Further investigation and the removal of debris showed an entrance in which a pool of water accumulated.
In the ensuing period, the water was drained away and a 400 feet passage was revealed ending in a boulder choke. The major breakthrough into the system beyond the entrance series occurred in 1984, before which the cave consisted of little more than the entrance series and several uninspiring passages. In 1986 Martyn Farr connected the Terminal Sump to Elm Hole in the next valley by cave diving. After decades of work and numerous cave digging projects, a connection to the nearby cave Ogof Agen Allwedd has yet to be found though they are only 75 metres away at their closest point. Cave description
The Clydach Gorge is a steep-sided valley in south-east Wales down which the River Clydach flows to the River Usk. It runs for 5.6 km from the vicinity of Brynmawr in Blaenau Gwent eastwards and northeastwards to Gilwern in Monmouthshire. The Gorge was one of the first locations in the region to be industrialised though it still retains its natural environment, it has long been an important transport corridor between Abergavenny and the lowlands of Monmouthshire and the northeastern quarter of the South Wales Coalfield. It is now exploited by the A465 Heads of the Valleys trunk road which runs between Abergavenny and Swansea and which serves the Heads of the Valleys sub-region; the Gorge is included within the Brecon Beacons National Park and is a tourist destination in its own right, with facilities including a picnic site, waymarked footpaths, the National Cycle Network and car parking alongside the River Clydach reached from the Heads of the Valleys Road. It includes Smart's Bridge, a cast iron bridge and the remains of a late 18th-century ironworks which are now a Scheduled Ancient Monument.
There are limeworks. The industrial town of Brynmawr sits at the head of the gorge and the large village of Gilwern sits at its foot in the Usk valley. Although development along the gorge and its sides is semi-continuous, the linear settlements of Clydach, Blackrock and Maesygwartha can be distinguished along the roads between Brynmawr and Gilwern to the north of the river; the settlement of Llanelly Hill occupies the northwest hilltop of the gorge. The Hanbury family of Pontypool established a furnace and forge here in the sixteenth century though nothing now remains of them other than parts of the masonry dam of a pool connected with the water power used for the forge. Wrought iron was made at the furnace from cast iron using charcoal. A tinworks operated at this site at one time; the Clydach Ironworks was the most significant ironworks developed in the Cwm Gorge. The Ironworks were constructed around 1793–95 after coke had been introduced as a fuel for blast furnaces. By 1841 the works was responsible for the employment of more than 1350 people though many of this number were associated with obtaining iron ore and coal further up the valley.
These ironworks had a great influence on the industrial and social developments of the surrounding area. Due to this, building began on buildings for settling the workers at the end of the 18th century, increasing house production during the 2nd quarter of the 19th century; the works could be approached over Smart's Bridge. Production continued up until around 1860; the works were associated with the Frere family. The remains of two large masonry furnaces from the 1790s and the base of a furnace can still be seen together with other structures thanks to an excavation carried out in 1986; these limeworks were the first established in the gorge, having started production in 1794/95. From Blackrock, the quarry extends along the contours of the gorge above Clydach North, they continued to work until 1908 and the masonry limekilns remain today. The limeworks at Clydach were built in 1877 to provide lime for the construction of the nearby Nant Dyar railway viaduct. Two pairs of limekilns remain against an impressive quarried backdrop.
Llanelly Quarry supplied the Clydach Ironworks with limestone, subsequently lime for farming and building mortars. It closed in 1962. Two pairs of limekilns remain alongside the Merthyr and Abergavenny Railway and National Cycle Route; this early railroad was constructed during 1793–4 by the engineer John Dadford. It linked Wain Dew colliery at Beaufort with Glangrwyne Forge on the banks of the River Usk. An important surviving feature of the railroad is the single-arched bridge of coarse rubble-stone near Maesygwartha, impressively set above a waterfall. A tramroad linked into the Clydach Ironworks from the Clydach Railroad by means of a cast-iron bridge. Constructed by Smart in 1824, it is one of the earliest in the world. Engineered by Thomas Dadford in 1793-4, this tramroad to link the Clydach ironworks with the coalmines and iron ore deposits at Gellifelen and Llam-march. There is a single-arched stone bridge at SO 233137 and SO 255176, the latter being the Llam-march Tramroad and Aqueduct Bridge of 1811 which carried water from the Clydach to the Clydach Ironworks Rolling Mill via a leat.
Engineered by Crawshay Bailey in 1821, this tramroad traverses the southeastern slopes of the gorge below and parallel to the Llam-march Tramroad. It connected the Bailey's ironworks at Nantyglo with the Monmouthshire and Brecon Canal at Govilon, in the Usk Valley. See main article on Merthyr and Abergavenny RailwayThe railway was constructed in 1862 as a single line, following in part, the line of an earlier tramroad. Four years it became a part of the London and North Western Railway network and in 1877 the line was doubled along its entire length; the routing of the line through the gorge was a considerable engineering challenge requiring the digging of several tunnels and the construction of an impressive curving viaduct across the ravine of the Nant Dyar. The line continued in operation until the 1950s when British Rail decided to close it as being uneconomical to run; the last trains ran along it in June 1958. The larger part of the track-bed has now been converted to a cycleway, forming part of r
Speleothems known as cave formations, are secondary mineral deposits formed in a cave. Speleothems form in limestone or dolostone solutional caves; the term "speleothem" as first introduced by Moore, is derived from the Greek words spēlaion "cave" + théma "deposit". The definition of "speleothem" in most publications excludes secondary mineral deposits in mines, tunnels and on man-made structures. Hill and Forti more concisely defined "secondary minerals". 319 variations of cave mineral deposits have been identified. The vast majority of speleothems are calcareous, composed of calcium carbonate in the form of calcite or aragonite, or calcium sulfate in the form of gypsum. Calcareous speleothems form via carbonate dissolution reactions. Rainwater in the soil zone reacts with soil CO2 to create weakly acidic water via the reaction: H2O + CO2 → H2CO3As the lower pH water travels through the calcium carbonate bedrock from the surface to the cave ceiling, it dissolves the bedrock via the reaction: CaCO3 + H2CO3 → Ca2+ + 2 HCO3−When the solution reaches a cave, degassing due to lower cave pCO2 drives precipitation of CaCO3: Ca2+ + 2 HCO3− → CaCO3 + H2O + CO2Over time the accumulation of these precipitates form stalagmites and flowstones, which compose the major categories of speleothems.
Calthemites which occur on concrete structures, are created by different chemistry to speleothems. Speleothems take various forms, depending on whether the water drips, condenses, flows, or ponds. Many speleothems are named for their resemblance to natural objects. Types of speleothems include: Dripstone is calcium carbonate in the form of stalactites or stalagmites Stalactites are pointed pendants hanging from the cave ceiling, from which they grow Soda straws are thin but long stalactites having an elongated cylindrical shape rather than the usual more conical shape of stalactites Helictites are stalactites that have a central canal with twig-like or spiral projections that appear to defy gravity Include forms known as ribbon helictites, rods, hands, curly-fries, "clumps of worms" Chandeliers are complex clusters of ceiling decorations Ribbon stalactites, or "ribbons", are shaped accordingly Stalagmites are the "ground-up" counterparts of stalactites blunt mounds Broomstick stalagmites are tall and spindly Totem pole stalagmites are tall and shaped like their namesakes Fried egg stalagmites are small wider than they are tall Columns result when stalactites and stalagmites meet or when stalactites reach the floor of the cave Flowstone is sheet like and found on cave floors and walls Draperies or curtains are thin, wavy sheets of calcite hanging downward Bacon is a drapery with variously colored bands within the sheet Rimstone dams, or gours, occur at stream ripples and form barriers that may contain water Stone waterfall formations simulate frozen cascades Cave crystals Dogtooth spar are large calcite crystals found near seasonal pools Frostwork is needle-like growths of calcite or aragonite Moonmilk is white and cheese-like Anthodites are flower-like clusters of aragonite crystals Cryogenic calcite crystals are loose grains of calcite found on the floors of caves, are formed by segregation of solutes during the freezing of water.
Speleogens are formations within caves that are created by the removal of bedrock, rather than as secondary deposits. These include: Pillars Scallops Boneyard Boxwork Others Cave popcorn known as "coralloids" or "cave coral", are small, knobby clusters of calcite Cave pearls are the result of water dripping from high above, causing small "seed" crystals to turn over so that they form into near-perfect spheres of calcium carbonate Snottites are colonies of predominantly sulfur oxidizing bacteria and have the consistency of "snot", or mucus Calcite rafts are thin accumulations of calcite that appear on the surface of cave poolsSpeleothems made of sulfates, mirabilite or opal occur in some lava tubes. Although sometimes similar in appearance to speleothems in caves formed by dissolution, lava stalactites are formed by the cooling of residual lava within the lava tube. Speleothems formed from salt and other minerals are known. Speleothems made of pure calcium carbonate are a translucent white color, but speleothems are colored by chemicals such as iron oxide, copper or manganese oxide, or may be brown because of mud and silt particulate inclusions.
Many factors impact the shape and color of speleothem formations including the rate and direction of water seepage, the amount of acid in the water, the temperature and humidity content of a cave, air currents, the above ground climate, the amount of annual rainfall and the density of the plant cover. Most cave chemistry revolves around calcium carbonate, the primary mineral in limestone and dolomite, it is a soluble mineral whose solubility increases with the introduction of carbon dioxide. It is paradoxical in that its solubility decreases as the temperature increases, unlike the vast majority of dissolved solids; this decrease is due to interactions with the carbon dioxide, whose solubility is diminished by elevated temperatures. Most other solution caves that are not composed of limestone or dolostone are composed of gypsum, the solubility of, positively c