As Tuff ( Italian tufo , from the same major Latin tofu ), illustrative, and tuff called, is known in the petrography a rock that more than 75% of pyroclastic consists of all grain sizes. The tuffs are volcanic igneous rock that has solidified. The colors of the volcanic tuffs that occur worldwide range from gray to yellowish, brownish and reddish to strong red. Due to the volcanic gas inclusions , tuff is often very porous. In the technical sense, almost all types are soft rock . For this reason, tuffs were used in the construction industry as masonry stones and tuff bricks, today mainly for panels on facades, for restoration work as well as for stone carving work.
Due to its cultural and historical importance, tuff was designated Rock of the Year 2011 in Germany .
According to the recommendation of the IUGS (International Union of Geological Sciences), a rock is called tuff or ash tuff if it consists of 75% volcanic ash (<0.2 cm) (the rest can also consist of coarser components) and a total of more than 75% consists of pyroclasts (the rest can also consist of components from other rocks). However, the term tuff was used much more broadly in the past and simply referred to solidified pyroclastic deposits of all grain sizes. In today's literature, too, tuff usually refers to a rock that not only consists of solidified volcanic ash, but also generally solidified pyroclastic deposits of various grain sizes. The term tuff should therefore be used in connection with grain size or genetic names.
If the proportion of pyroclasts in the rock is only between 25 and 75%, the rock is referred to as tuffite . The recommendation of the IUGS ( International Union of Geological Sciences ) to reserve the term only for rocks that consist of volcanic ash (grain size less than 0.2 cm) has not yet been implemented.
In contrast to volcanic tuffs, limestone tuffs are formed from limestone deposits.
According to grain sizes
The term tuff is combined with terms derived from the grain size classification of pyroclastic rocks or sediments.
- Tuff breccia is a pyroclastic rock made up of between 25% and 75% volcanic bombs and blocks, the remainder can be lapilli and / or volcanic ash.
- Lapilli tuff is a pyroclastic rock that contains less than 25% volcanic bombs and volcanic blocks and more than 75% lapilli and volcanic ash.
- Ash tuff, 75% of the components must consist of volcanic ash (<0.2 cm). Often there is a further subdivision into coarse ash tuff and fine ash tuff.
According to components
Tuffs (and especially ash tuffs) can also be broken down more precisely according to their components:
- Lithic tuff (also slag tuff) consists mainly of rock fragments,
- Vitreous tuff consists mainly of pumice as well as glass fragments and
- Crystal tuff consists mainly of (single) crystals. It occurs almost exclusively as ash tuff.
Some authors also use very specific component names such as obsidian tuff or pumice (stone) tuff, where pumice tuff is a pleonasm.
According to the chemical-mineralogical composition
Tuffs can also be designated by their mineralogical-chemical composition by adding appropriate additives. Tuffs or ignimbrites, which chemically and mineralogically correspond to a rhyolite , can accordingly be referred to as rhyolite tuffs or rhyolithic ignimbrites. Correspondingly, terms such as basaltic , andesitic and dazitic tuffs can also be formed. As an alternative to this example, tuffs can also be referred to as basaltic, andesitic or dazitic composition.
According to genesis
Tuffs made from pyroclastic falling deposits and tuffs made from pyroclastic flow deposits often differ very clearly from each other, especially in terms of density, hardness and thus machinability. This is mainly due to the very different temperature. The temperature of the pyroclastic flow deposits is, in contrast to the pyroclastic fall deposits, often very high.
After the deposit, the contained components can be partially melted and literally "welded" together as they cool down. Welded tuffs made of pyroclastic flow deposits are also called melting tuffs or ignimbrite (from Latin ignis "fire", imber "rain"); Ignimbrite is therefore only a special formation of a tuff. Ignimbrites usually consist of very compact, often quite thick layers, which correspond to one or more current events in rapid succession. Molten tuffs or ignimbrites are often difficult to distinguish from lava with the naked eye .
Some authors refer to all pyroclastic current deposits, whether fused or normally solidified, as ignimbrites.
Light ashes that are thrown to a height of many kilometers are often displaced thousands of kilometers and can lead to the deposition of ash tuff (or ash tuff) in areas far from the center of the eruption. Tuff and tuff are easily identified in drill core and are suitable for relative and absolute dating as well as for correlating profiles.
Economic importance and natural stone
Tuff is generally a relatively soft rock (exception: melted tuff) and can therefore be easily processed as natural stone. Due to its insulating property (caused by gas inclusions), it is often used as a building material. Especially in the area around Rome and Naples , where the so-called peperin was used as a building material in ancient times , many buildings can still be found today that were built from this tuff.
In Germany, tuffs were not only used locally as solid building blocks in the building industry; for example, tuffs from the Eifel are widespread along waterways due to their proximity to the Rhine. Examples of this are the town hall in Koblenz , Cologne Cathedral and numerous houses in Koblenz .
The building of the St. Nicolai Church in Hollingstedt in Schleswig-Holstein is made of tuff that was brought from the Eifel to Hollingstedt via the Rhine , North Sea , Eider and Treene . From there the tuff made its way to Denmark .
Today, tuffs are mainly used outdoors as facade panels and window sills, boss stones and regionally as tuff bricks. They are important in the preservation of monuments and they are also worked into sculptures by sculptors . Riedener tuff is a specialty in its use, because this tuff was mainly used in furnace construction because of its heat storage. Tufa bricks are also used for high-quality raised beds - see private vegetable gardens.
Here are some examples:
- Weiberner Tuff ( Weibern , Eifel)
- Ettringer Tuff ( Ettringen , Eifel)
- Riedener Tuff ( Rieden , Eifel)
- Tufo giallo ( Viterbo , Latium , Italy)
- Rochlitz Porphyry ( Rochlitz , Saxony)
- Hilbersdorfer Porphyrtuff ( Chemnitz , Saxony)
In Cappadocia, numerous settlements emerged in mighty tufa layers that were driven into the tuff.
Rock of the year
The professional association of German geoscientists e. V. and the German Society for Geosciences have chosen tuff as rock of the year 2011. In the reason for the choice it is particularly emphasized that tuff rocks are not only scientifically interesting. Through their use as cement or as stone for buildings, tuffs have and still were of great importance for the architectural history of Germany.
- Roger Walter Le Maitre: Igneous rocks: IUGS classification and glossary; recommendations of the International Union of Geological Sciences, Subcommission on the Systematics of Igneous Rocks . 2nd Edition. Cambridge University Press, New York 2002, ISBN 0-521-66215-X .
- Walter Maresch, Olaf Medenbach: Steinbach's natural guide. Rocks . Mosaik-Verlag, Munich 1996, ISBN 3-576-10699-5 , pp. 142 ff .
- Roland Vinx: Rock determination in the field . 2nd Edition. Springer-Verlag, Berlin Heidelberg 2008, ISBN 978-3-8274-1925-5 .
- Hans Pichler, Thomas Pichler: volcanic areas of the earth . Spectrum Akademischer Verlag, Heidelberg 2007, ISBN 978-3-8274-1475-5 .
- Holger Schaaff: An old mine and an experiment - on the ancient and medieval technology of tuff extraction . In: Archaeological correspondence sheet . 2011, p. 531–542 ( uni-heidelberg.de [PDF; 1.4 MB ; accessed on November 30, 2019]).