Travertine
What is travertine?
Travertine is a sedimentary rock.
It is a natural chemical precipitate of carbonate minerals; typically
Aragonite, but often recrystallized to, or primarily, Calcite.
The way travertine forms is basically this: 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.
Formation
When carbon dioxide-rich water
percolates through rocks in limestone areas, the water dissolves the
limestone (typical karst process) and becomes saturated with it. When
the environment the water runs through changes significantly, (e.g. drop
in pressure and/or change in temperature) this causes the water to
release the carbon dioxide as gas, much like fizzy drinks. The calcium
carbonate then recrystallizes; small debris, scrub 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 exceptionally porous, it is known as calcareous
tuff[citation needed] (German: Kalktuff). When pure and fine, travertine
is white, but often is brown to yellow due to impurities (other than
carbonate minerals).
Occurrence
Extensive deposits exist at Tivoli,
Italy, near Rome. In fact, 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 16 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.
Photos courtesy of DTS