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Amazing World of Travertine

In the sixth of our series of blogs about the origins of natural stone, we are looking at where travertine comes from. It is a natural sedimentary rock that is most often found in Italy but travertine deposits are also common in Turkey, Mexico, Peru, Croatia, Iran, USA and even China. The quality and characteristic of travertine differ depending on the region of its origin due to the different geology there.

Etymology

The word ‘travertine’ is derived from the Italian travertino, itself a derivation of the Latin tiburtinus ‘of Tibur’. Its namesake is also the origin of Tivoli, a district near Rome.

Formation of Travertine 

Formed in geothermal springs, travertine is often connected to siliceous structures that form siliceous sinter. Colonial organisms such as macrophytes, bryophytes, algae, cyanobacteria often preserve the exterior surface of travertine by covering it and providing it with its porous texture.

In some hot springs, the high temperature eliminates the macrophytes and bryophytes from the deposits. As a result of the exclusion the deposits turn out to be less permeable than tufa. Thermophilic microbes are important in these environments and stromatolitic fabrics are more abundant. Deposits that are evidently lacking any biological component are often referred to as calcareous sinter.

Elevated levels of carbon dioxide and geothermally heated supersaturated basic waters are two mandatory requirements for the formation of contemporary travertine. The waters later de-gas carbon dioxide due to the lower atmospheric carbon dioxide, resulting in an upsurge in pH levels.

Decrease in increased basic nature, caused by carbonate solubility, induces precipitation. The precipitation process may be influenced by multiple factors leading to a drop in carbon dioxide, for example, an increment in the air and water interaction at waterfalls may be as important as photosynthesis. In some hot springs, precipitation may be boosted by evaporation.

Two types of carbonate minerals found in travertine hot springs are calcite and aragonite. Calcite is dominant at lower temperatures, while higher temperatures are more accommodating for aragonite. Travertine in its purest form is white but is often brown to yellow due to impurities.

Geochemistry

Modern travertine is formed from geothermally heated supersaturated alkaline waters, with raised pCO2. On emergence, waters degas CO2 due to the lower atmospheric pCO2, resulting in an increase in pH. Since carbonate solubility decreases with increased pH, 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, as may photosynthesis. 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. 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 Mammoth Hot Springs for example.

Travertine Occurrence, Quarries and Supply  

About 30 years ago, until the 1980s, Italy was the main supplier of travertine and had a monopoly on the market. The most famous quarries in Italy are in Guidonia Montecelio and in Tivoli, while the name of the latter district and the word travertine have the same origin from the Latin word tiburtinus through the Italian travertino. The natural stone was quarried in Italy since Ancient Roman times and was used primarily as building material. Nowadays, significant travertine suppliers are Turkey, Mexico, Peru and Iran. There are two-three small producers in the USA, in its western part and the most famous place for travertine formation, that is also visited by many tourists is Yellowstone National Park. There are also two parks dedicated to this natural stone in Oklahoma. Pamukkale in Turkey is also one of the beloved tourist destinations, which attracts with its vast white panorama. Its name means “cotton castle” derived from the look of the rocks and consists of hot springs and travertine terraces. Another huge travertine deposit in Europe is located in Croatia in the valley known as Plitvice Lakes National Park. It took travertine several millennia to form sixteen huge natural lakes and several waterfalls, the highest one falling from 70 m to the ground.

Travertine Usage  

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, the largest building in the world constructed mostly of travertine. The Shroud of Turin, when examined by Joseph Kohlbeck from the Hercules Aerospace Company in Utah and Richard Levi-Setti of the Enrico Fermi Institute, was found to contain particles of travertine aragonite limestone.

Travertine regained popularity as a building material in the Middle Ages. The central German town of Bad Langensalza has an extant medieval old town built almost entirely of local travertine.

Notable 20th Century buildings using travertine extensively include the Sacré-Cœur Basilica in Paris, the Getty Center in Los Angeles, California, and Shell-Haus in Berlin. The travertine used in the Getty Center and Shell-Haus constructions was imported from Tivoli and Guidonia.

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. 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, the Farnsworth House and the Barcelona Pavilion.

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