Speleothem
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As speleothem or cave mineral designates speleologist each secondary mineral deposition in caves ; but it can also develop in other moist cavities such as mines and tunnels. The most common speleothems are cave sinter ( sinter ) or stalactites . They mostly consist of the minerals calcite and aragonite or the compound calcium carbonate (lime), and various forms of gypsum are also common . Speleothems made of opal also occur in suitable rocks such as sandstone or quartzite .
There are thousands of different forms of speleothemes. However, most of these are extremely rare and only appear in a few caves in the world.
Origin of the term
There is also a German word for speleothem, the cave mineral. This term is currently increasingly being replaced by speleothem, a combination of the Greek words σπηλαίων ( spelaion , cave) - which is used in the terms speleology and speleologist (cave explorer) - and θέμα ( subject , deposit).
The term was coined in 1952 by the American cave explorer GW Moore and is primarily used by geologists and speleologists to achieve an internationally uniform language.
Delimitation of the terms
The terms speleothem and the well-known stalactite classify the minerals according to different criteria. This requires a more detailed explanation of the differences.
Formations resulting from the redistribution of material in the rock mostly consist of minerals . A subset of this occurs in caves and is therefore naturally referred to as cave mineral. Dripstones are created by dripping water, more precisely by the precipitation of previously dissolved material from the water. The name suggests that the water is flowing, which leads to the formation of mineral forms other than standing water.
The two terms stalactite and speleothem therefore have a considerable overlap, namely the stalactites formed in caves. Since stalactites can also arise in mines and buildings and there are minerals in caves that were not formed in flowing water, there are both stalactites that are not speleothems and, conversely, speleothems that are not stalactites. In this context, it is therefore often incomprehensible that stalactites in mines are naturally formed minerals, but not speleothems in the narrower sense because they were formed in other cavities.
Common speleothems
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Stalactites
- Canopies
- Ceiling sintering strip
- Button sinter (pearl sinter, cauliflower sinter)
- Macaroni (sinter tubes, tube sinter - image area B )
- Sinter vane (sinter curtain) (image area F )
- Sinter (sinter crust)
- Sinter basin (image area J )
- Sintered ceiling
- Sinter fall
- Stalagmite (image area C )
- Stalagnate (stalactite column - image area E )
- Stalactite (image area A )
- Sintered wall wreath
- Wall sintering strip
- Special forms
- Boxwork
- Excentrique (image area H )
- Gypsum flower
- Cave pearl
- Calcareous membrane
- Moon milk (image area I )
Special forms
Cave pearls
First, drops are hollowed out on a soft ground by means of drops, which are sintered by limescale deposits. In these water basins, cave pearls are formed when lime is deposited around a condensation core made of sediment particles or rock fragments. Constant movement of the water, such as dripping water, causes this grain to be continuously rotated. Layers of lime sinter (often also aragonite ) are slowly deposited. If the cave bead becomes too heavy so that it no longer moves, it can also grow into place. The pea stone consists of such collections of cave pearls .
Calcareous membrane
Lime membranes consist of small calcite crystals that float on the water of a sinter basin. If they get too heavy, they go under and form very characteristic puff pastry-like deposits.
Opal speleothems
In silicate rocks such as sandstone and quartzite, speleothems that do not consist of carbonate but of silicates such as opal or quartz can occur under special conditions. Examples of such formations can be found particularly widespread in the caves of the South American tepuis, such as in the Muchimuk cave system or in the Cueva Ojos de Cristal des Roraima-Tepuis . More than a dozen forms of mushroom, kidney or ball shape, also coral-like and irregularly branched, have been described.
The occurrence of these formations is explained by the evaporation of cave water with the accumulation of dissolved silicon dioxide and the precipitation of finely atomized water on walls and ceilings outside the influence of flowing water. The precipitation of opal was also observed on cobwebs, which collapsed from the heel of the material and formed stalactite-like shapes.
Bacteria that can be detected in the material of the speleothemes play a special role in the formation of the opal speleothemes.
literature
- Carol A. Hill, Paolo Forti: Cave Minerals of the World . Ed .: National Speleological Society . 2nd Edition. 1997, ISBN 978-1-879961-07-4 .
- GW Moore: Speleothem - A new Cave Term . In: National Speleological Society of the USA News . tape 10 , no. 6 , 1952, pp. 2 .
Web links
- Mineral Atlas: Speleothem
- Overview of Speleothems (English)
- Cave plans and UIS symbol list for cave signatures ( Memento from March 25, 2016 in the Internet Archive ) (PDF file; 342 kB)
Individual evidence
- ^ Piet Nordhoff: Speleothems, U-series dating and growth frequency analysis. (PDF file, 164 KB) (No longer available online.) Archived from the original on February 3, 2015 ; Retrieved on December 17, 2009 (Excursion Guide Hydrogeological Excursion Lebanon, Faculty of Geosciences and Geography - Geoscientific Center, Georg-August-Universität Göttingen).
- ^ Carol A. Hill and Paolo Forti: Cave mineralogy and the NSS: past, present, future . In: Journal of Cave and Karst Studies . tape 69 , no. 35 , April 2007, p. 36 ( online version; 2.1 MB ).
- ↑ a b Roman Aubrecht, Charles Brewer-Carias, Branislav Šmída, Marek Audy, Ľubomír Kováčik: Anatomy of biologically mediated opal speleothems in the world's large largest sandstone cave Cueva Charles Brewer, Chimantá Plateau, Venezuela . In: Sedimentary Geology . tape 203 , no. 3-4 . Amsterdam 2008, p. 181-195 . ( Page no longer available , search in web archives: online version; PDF file; 6.4 MB )