Travertine
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Travertine is a sedimentary rock. It is a natural chemical precipitate of carbonate minerals; typically aragonite, but often recrystallized to, or primarily, calcite.
Travertine forms as calcium carbonate is deposited from the water of mineral springs or rivulets that are saturated with dissolved calcium bicarbonate. The spring water from which the calcium carbonate precipitates can be hot, warm or cold. The rate of deposition increases with the temperature of the water, or alternatively, when biotic material accelerates the process of precipitation.
The ornate columns of travertine in caves are an example of an inorganic chemical sedimentary rock.
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[edit] Formation
When carbon dioxide-rich water percolates through rocks in limestone areas, the water dissolves the limestone (typical karst process) and becomes saturated. A drop in pressure and/or change in temperature causes the water to release the carbon dioxide as gas, much like carbonated beverages. The calcium carbonate then recrystallizes and small debris and living biotic material such as moss, algae, and cyanobacteria become encrusted. The biotic material may survive, and may continue growing on top.
Rich deposits of aged, dried and hardened travertine were mined by the Romans. The rock typically remains quite porous with numerous cavities. When pure and fine, travertine is white, but often it is brown to yellow due to impurities (other than carbonate minerals).
[edit] Occurrence
Extensive deposits exist at Tivoli, Italy, near Rome. Travertine derives its name from this town. Tivoli was known as Tibur in ancient Roman times. The ancient name for the stone was lapis tiburtinus, meaning tibur stone, which has been corrupted to travertine.
Detailed studies of the Tivoli travertine deposits revealed diurnal and annual rhythmic banding and laminae which have potential use in geochronology.[1]
In Central Europe's last postglacial palaeoclimatic optimum (Atlantic Period, 8000-5000 B.C.), huge deposits of tufa formed from karst springs. Important geotopes are found at the Swabian Alb, mainly in valleys at the foremost northwest ridge of the cuesta, in many valleys of the eroded periphery of the karstic Franconian Jura, at the northern Alpine foothills, and the northern Karst Alps. On a smaller scale these karst processes are still working. Travertine was a very important building material for housing and representative buildings since the Middle Ages.
Travertine has formed sixteen huge, natural dams in a valley in Croatia known as Plitvice Lakes National Park. The travertine clings to moss and rocks in the water, and has built up over several millennia to form waterfalls up to 70 m in height.[2]
Other beautiful cascades of natural lakes formed behind travertine dams can be seen in Band-i-Amir (Afghanistan), HuangLong Valley (Sichuan, China), Semuc Champey (Guatemala), and Pamukkale (Turkey). Many geyser fields also have colorful travertine deposits.
[edit] Use as a building material
Travertine is often used as a building material. The largest building in the world constructed mostly of travertine is the Colosseum in Rome. Other notable buildings using travertine extensively include the Sacré-Cœur Basilica in Paris and the Getty Center in Los Angeles, California. The travertine used in the Getty Center construction was imported from Tivoli.[3]
Travertine is one of several natural stones that are used for paving patios and garden paths. It is sometimes known as travertine limestone, sometimes as travertine marble; these are the same stone, even though it is neither limestone nor marble. The stone is characterised by pitted holes and troughs in its surface. Although these troughs occur naturally, they suggest to some eyes that considerable wear and tear has occurred over many years. Some installers use a grout to fill these holes, whereas others leave them open — travertine can even be purchased "filled" or "unfilled." It can be effectively polished to a smooth, shiny finish and comes in a variety of colors from grey to coral-red. Travertine is most commonly available in tile sizes for floor installations.
Travertine is one of the most frequently used stones in modern architecture, and is commonly seen as façade material, wall cladding, and flooring. The lobby walls of the modernist Sears Tower in Chicago, Illinois are travertine.[4] Architect Welton Becket was one of the most frequent users of travertine, incorporating it extensively into many if not most of his projects. The entire first floor of the Becket-designed UCLA Medical Center has thick travertine walls.
There are two or three small travertine producers in the western United States. U.S. demand for travertine is about 0.85 million tons, almost all of it imported. Most of the imports come from Turkey, Mexico, Italy, and Peru. A decade ago, Italy had a near monopoly on the world travertine market.
[edit] References
- ^ Folk, R. L., et al.; (1985) Bizarre forms of depositional and diagenetic calcite in hot spring travertines, in Carbonate Cements; SEPM Special Pub. 36.
- ^ Nature . Land Of The Falling Lakes | Pbs
- ^ The Getty Center http://www.getty.edu/visit/see_do/architecture.html
- ^ The Sears Tower http://www.searstower.com/interior_exterior.html
- Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., Wiley, p. 496 ISBN 0-471-80580-7
[edit] See also
[edit] External links
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