Listing description
Travertine is a
terrestrial sedimentary rock, formed by the precipitation of carbonate minerals from solution in
ground and surface waters, and/or geothermally heated hot-springs.[1][2] Similar (but softer
and extremely porous) deposits formed from ambient-temperature water are known
as tufa.
Features
Travertine forms
from geothermal springs and is often linked to siliceous systems that form siliceous sinter. Macrophytes, bryophytes, algae,cyanobacteria, and other organisms often colonise the surface of travertine
and are preserved, giving travertine its distinctive porosity.
Some springs have
temperatures high enough to exclude macrophytes and bryophytes from the
deposits. As a consequence, deposits are, in general, less porous than tufa. Thermophilic microbes are
important in these environments and stromatolitic fabrics are common.
When it is apparent that deposits are devoid of any biological component, they
are often referred to as calcareous sinter.
Geochemistry[edit]
Modern travertine is
formed from geothermally heated supersaturated alkaline waters, with raised pCO2 (see partial pressure). On emergence,
waters degas CO2 due
to the lower atmospheric pCO2, resulting in an increase in pH. Since
carbonate solubility decreases with increased pH,[3] precipitation is
induced. Precipitation may be enhanced by factors leading to a reduction in pCO2,
for example increased air-water interactions at waterfalls may be important,[4] as may
photosynthesis.[5] Precipitation may
also be enhanced by evaporation in some springs.
Both calcite and
aragonite are found in hot spring travertines; aragonite is preferentially
precipitated when temperatures are hot, while calcite dominates when
temperatures are cooler.[6][7] When pure and fine,
travertine is white, but often it is brown to yellow due to impurities.
Travertine may
precipitate out directly onto rock and other inert materials as in Pamukkale or Yellowstone for example.
Occurrence
In Italy, well-known travertine quarries exist in Tivoli and Guidonia Montecelio, where the most important quarries since Ancient Roman times,
like the old quarry of Bernini in Guidonia, can be found.[8] The latter has a
major historic value, because it was one of the quarries that Gian Lorenzo Bernini selected material
from to build the famous Colonnade of St. Peter's Square
in Rome (colonnato di Piazza S. Pietro) in 1656-1667.Michaelangelo also chose
travertine as the material for the external ribs of the dome of St Peter's Basilica.[9] Travertine derives
its name from the former town, known as Tibur in ancient Roman times. The
ancient name for the stone was lapis
tiburtinus, meaning tibur
stone, which was gradually corrupted to travertine. Detailed studies of the
Tivoli and Guidonia travertine deposits revealed diurnal and annual rhythmic
banding and laminae, which have potential use in geochronology.[10]
Cascades of natural
lakes formed behind travertine dams can be seen in Pamukkale, Turkey, which is a UNESCO World
Heritage Site. Other places with such cascades include Huanglong in Sichuan Province of China (another UNESCO World Heritage Site),
the Mammoth Hot Springs in the USA, Egerszalók in Hungary, Mahallat, Abbass Abad, Atash
Kooh, and Badab-e Surt in Iran, Band-i-Amir in Afghanistan, Lagunas de Ruidera,Spain, and Semuc Champey, Guatemala.
In Central Europe's last post-glacial
palaeoclimatic optimum (Atlantic Period, 8000-5000 B.C.), huge deposits of tufa formed from karst springs.[citation needed] 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 has been an important building material since the Middle Ages.
Travertine has
formed sixteen huge, natural dams in a valley in Croatia known as Plitvice Lakes National Park.
Clinging to moss and rocks in the water, the travertine has built up over
several millennia to form waterfalls up to 70 metres (230 ft) in height.[11]
In the U.S., the most
well-known place for travertine formation is Yellowstone National
Park, where the geothermal areasare rich in travertine deposits.[12] Oklahoma has two parks
dedicated to this natural wonder. Turner Falls, the tallest
waterfall in Oklahoma, is a 77 feet (23 m) cascade of spring water flowing
over a travertine cave. Honey Creek feeds this waterfall and creates miles of
travertine shelves both up and downstream. Many small waterfalls upstream in
the dense woods repeat the travertine-formation effect. The city of Davis now
owns thousands of acres of this land and has made it a tourist attraction.
Another travertine resource is in Sulphur, Oklahoma, 10 miles
(16 km) east of Turner Falls. Travertine Creek flows through a
spring-water nature preserve within the boundaries of the Chickasaw National
Recreation Area.[citation needed]
In Texas, the city of Austin and its surrounding
"Hill Country" to the south is built on limestone. The area has many
travertine formations, such as those found at Gorman Falls within Colorado Bend State
Park, the nature preserve known as Hamilton Pool, the West Cave
Preserve, and Krause Springs in Spicewood.
Hanging Lake in Glenwood Canyon in Colorado has travertine
deposits and aqua blue water. Rifle Falls State Park in Colorado features
a triple waterfall over a travertine dam.[13]
In Arizona, on the south side
of the Grand Canyon there is the Havasupai Reservation. Flowing through it is Havasu Creek, which has
extensive travertine deposits.[citation needed]Three major waterfalls, Navajo Falls, Havasu Falls,
and Mooney Falls, are all located downstream from the town of Supai. There are
numerous smaller cataracts formed by travertine dams. These features are
located about 2 miles from Supai Village (on the floor of the canyon), and are
accessible by foot or horseback.
In Iceland, the Hvanná river,
located at the north flank of the Eyjafjallajökull, was heavily charged with CO2 following the 2010 eruptions. Travertine precipitated along the river.[14]By 2014, CO2 concentration in the river has
decreased and travertine has started to dissolved. However, in places, where
the river changed its bed, travertine covered rocks can still be seen.
In North East
Sulawesi, Indonesia is the Wawolesea Karst. A notable feature of this area is a pond several meters from
the beach, formed by a salty, hot water fountain extant since the Neogene period.[15]
Uses[edit]
Travertine is often
used as a building material. The Romans mined
deposits of travertine for building temples, aqueducts, monuments, bath
complexes, and amphitheaters such as the Colosseum,[16] the largest building
in the world constructed mostly of travertine.
Other notable
buildings using travertine extensively include the Sacré-Cœur Basilica in Paris and the 20th-century Getty Center in Los Angeles, California, and Shell-Haus inBerlin. The travertine used in the Getty Center and
Shell-Haus constructions was imported from Tivoli and Guidonia.[17]
Travertine is one of
several natural stones that are used for paving patios and garden paths. It is
sometimes known as travertine limestone or travertine marble; these are the
same stone, although travertine is classified properly as a type of limestone,
not marble. The stone is characterised by pitted holes and
troughs in its surface. Although these troughs occur naturally, they suggest
signs of considerable wear and tear over time. It can also be 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. It is commonly used for façades, wall cladding, and flooring. The lobby walls of the modernist Willis Tower (1970) (formerly
Sears Tower) in Chicago are made of
travertine.[18] Architect Welton Becket frequently
incorporated travertine into many of his projects. The first floor of the Becket-designed UCLA Medical Center has thick travertine
walls. Architect Ludwig Mies van der
Rohe used travertine in several of his major works, including the Toronto-Dominion Centre, S.R. Crown Hall and the Farnsworth House.
Detailed description
Apatite is a group of phosphate
minerals, usually
referring to hydroxyapatite, fluorapatite, chlorapatite and bromapatite, named for high concentrations of OH−, F−, Cl− or Br− ions, respectively, in the crystal. The formula of the admixture of the
four most common endmembers is written as Ca10(PO4)6(OH, F, Cl, Br)2,
and the crystal unit cell formulae of the individual minerals are written as Ca10(PO4)6(OH)2,
Ca10(PO4)6(F)2, Ca10(PO4)6(Cl)2
and Ca10(PO4)6(Br)2.
Apatite is one of
a few minerals that are produced and used by biological micro-environmental
systems. Apatite is the defining mineral for 5 on Mohs Scale hardness. Hydroxyapatite, also known as
hydroxylapatite, is the major component of tooth enamel and bone mineral. A relatively rare form of apatite in
which most of the OH groups are absent and containing many carbonate and acid
phosphate substitutions is a large component of bone material.
Fluorapatite (or
fluoroapatite) is more resistant to acid attack than is hydroxyapatite. For
this reason, toothpaste typically contains a source of fluoride anions (e.g. sodium fluoride, sodium
monofluorophosphate).
Similarly, fluoridated
water allows exchange
in the teeth of fluoride ions for hydroxyl groups in apatite. Too much fluoride results
in dental
fluorosis and/or skeletal
fluorosis.
Fission
tracks in apatite are
commonly used to determine the thermal history of orogenic (mountain) belts and
of sediments in sedimentary
basins. (U-Th)/He dating of apatite is also well-established
for use in determining thermal histories and other, less typical applications
such as paleo-wildfire dating.
Phosphorite is a phosphate-rich sedimentary rock, that contains between 18% and 40% P2O5.
The apatite in phosphorite is present as cryptocrystalline masses referred to as collophane.
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Uses
The primary use
of apatite is in the manufacture of fertilizer - it is a source of phosphorus.
It is occasionally used as a gemstone.
Fluoro-chloro
apatite forms the basis of the now obsolete Halophosphor fluorescent tube
phosphor system. Dopant elements of manganese and antimony, at less than one
mole-percent, in place of the calcium and phosphorus impart the fluorescence,
and adjustment of the fluorine to chlorine ratio adjusts the shade of white
produced. Now almost entirely replaced by the Tri-Phosphor system.[3]
In the United States, apatite derived fertilizers are used
to supplement the nutrition of many agricultural crops by providing a valuable
source of phosphate.
Gemology
Apatite is
infrequently used as a gemstone. Transparent stones of clean color have been
faceted, and chatoyant specimens have been cabochon cut.[1] Chatoyant stones are known as cat's-eye
apatite,[1] transparent green stones are known as
asparagus stone,[1] and blue stones have been called moroxite.[4] Crystals of rutile may have grown in
the crystal of apatite so when in the right light, the cut stone displays a
cat's eye effect. Major sources for gem apatite are[1] Brazil, Burma, and Mexico. Other sources include[1] Canada, Czechoslovakia, Germany, India, Madagascar, Mozambique, Norway, South Africa, Spain, Sri Lanka, and the United States.
Use as an ore mineral
Apatite is
occasionally found to contain significant amounts of rare
earth elements
and can be used as an ore for those metals [5]. This is preferable to traditional
rare earth ores, as Apatite is non-radioactive [6] and does not pose an environmental
hazard in mine
tailings.
Thermodynamics
The standard (p =
0.1 MPa) molar enthalpies of formation in the crystalline state of hydroxyapatite,
chlorapatite and a preliminary value for bromapatite, at T = 298.15 K, have
already been determined by reaction-solution calorimetry. Speculations on the
existence of a possible fifth member of the calcium apatites family,
iodoapatite, have been drawn from energetic considerations.[8]
Lunar science
Moon rocks collected by astronauts during the Apollo program contain traces of apatite.[9] Re-analysis of these samples in 2010
revealed water trapped in the mineral as hydroxyl, leading to estimates of water on the
lunar surface at a rate of at least 64 parts per billion – 100 times greater
than previous estimates – and as high as 5 parts per million.[10] If the minimum amount of
mineral-locked water was hypothetically converted to liquid, it would cover the
Moon's surface in roughly one meter of water.[11]
A
phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic
chemistry, a phosphate, or organophosphate,
is an ester
of phosphoric acid. Organic phosphates are important in biochemistry
and biogeochemistry or ecology.
Inorganic phosphates are mined to obtain phosphorus for use in agriculture and
industry.[1][2][3]
At elevated temperatures in the solid state, phosphates can condense to form pyrophosphates.|
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Chemical properties
This is the structural
formula of the phosphoric acid functional group as found in a weakly acidic aqueous solution. In more basic aqueous solutions, the group donates the two hydrogen
atoms
and ionizes
as a phosphate group with a negative charge of 2. [4]
The
phosphate ion is a polyatomic ion with the empirical
formula PO3−4 and a molar
mass of 94.973 g/mol. It consists of one central phosphorus
atom surrounded by four oxygen atoms in a tetrahedral
arrangement. The phosphate ion carries a negative three formal charge and is
the conjugate base of the hydrogen phosphate ion, HPO2−4, which is the conjugate base of H2PO−4,
the dihydrogen phosphate ion, which in turn is the conjugate base of H3PO4, phosphoric
acid. It is a hypervalent molecule (the phosphorus atom has 10
electrons in its valence shell). Phosphate is also an organophosphorus
compound with the formula OP(OR)3. A phosphate salt forms when a
positively-charged ion attaches to the negatively-charged oxygen atoms of the
ion, forming an ionic compound.
Many phosphates are not soluble in water at standard temperature and pressure.
The sodium, potassium, rubidium, caesium and ammonium phosphates are all water
soluble. Most other phosphates are only slightly soluble or are insoluble in
water. As a rule, the hydrogen and dihydrogen phosphates are slightly more
soluble than the corresponding phosphates. The pyrophosphates
are mostly water soluble.
Biochemistry of phosphates
In
biological systems, phosphorus is found as a free
phosphate ion in solution and is called inorganic phosphate, to
distinguish it from phosphates bound in various phosphate esters. Inorganic
phosphate is generally denoted Pi and at physiological
(neutral) pH
primarily consists of a mixture of HPO2−4 and H2PO−4 ions.Inorganic phosphate can be created by the hydrolysis of pyrophosphate, which is denoted PPi:
However, phosphates are most commonly found in the form of adenosine phosphates, (AMP, ADP and ATP) and in DNA and RNA and can be released by the hydrolysis of ATP or ADP. Similar reactions exist for the other nucleoside diphosphates and triphosphates. Phosphoanhydride bonds in ADP and ATP, or other nucleoside diphosphates and triphosphates, contain high amounts of energy which give them their vital role in all living organisms. They are generally referred to as high energy phosphate, as are the phosphagens in muscle tissue. Compounds such as substituted phosphines have uses in organic chemistry but do not seem to have any natural counterparts.
The addition and removal of phosphate from proteins in all cells is a pivotal strategy in the regulation of metabolic processes.
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