Tuff

Tuff (Italian tufo, from the same major Latin tofu ) is the colloquial abbreviation of tuff. Tuff referred to in the petrography a rock that consists of more than 75 % of pyroclastics of all grain sizes. The tuffs are volcanic igneous rock that solidified. The colors of the world occurring volcanic tuffs range from gray to yellowish, brownish and reddish to bright red. Due to the volcanic gas inclusions Tuff is often very porous. In the technical sense it is almost for all types of soft stones. Therefore tuffs were formerly often used in construction as bricks and Tuffziegel, today especially for plates on exterior facades, for restoration work as well as for stone sculptures.

Because of its cultural and historical significance in Germany was determined for Tufa rock of 2011.

Definition

Following the recommendation of the IUGS ​​(International Union of Geological Sciences), a rock is called tuff or ash tuff, if it is 75 % of volcanic ash (< 0.2 cm) ( the rest can also consist of coarser components) and a total of more than 75 % of pyroclastics is (the rest can also consist of components from other rocks consist ). However, the term tuff was formerly used generally much more comprehensive and designated simply solidified pyroclastic deposits of all grain sizes. Even in today's literature called Tuff usually a rock that consists not only of solidified volcanic ash, but in general solidified pyroclastic deposits of different grain size. The term should therefore be better tuff each used in conjunction with grain sizes or genetic designations.

If the fraction of pyroclasts in the rock only between 25 and 75% the rock is referred to as Tuffit. The recommendation of the IUGS ​​(International Union of Geological Sciences) to reserve the term for rocks from volcanic ash (particle size less than 0.2 cm) exist, has not been enforced.

Kalktuffe arise in contrast to the volcanic tuffs of limescale.

Subdivision of the term according to particle size

The term Tuff is combined with terms that originate from the grain size classification of pyroclastic rocks or sediments.

• Tuff breccia is a pyroclastic rock composed of between 25 % and 75 % of volcanic bombs and blocks, the rest 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). Frequently still takes place a further breakdown in Coarse ash tuff and ash tuff Fine.

Breakdown of tuffs by component

Tuffs (and especially Aschentuffe ) can be broken down in more detail and for its components.

• Lithic tuff consists predominantly of rock fragments
• Vitrischer Tuff consists mainly of pumice and glass fragments
• Kristalltuff consists mainly of (single) crystals. It occurs almost exclusively as ash tuff.

Some authors also use direct very specific component designations such as pumice ( stone ) tuff, which in turn Bimssteintuff is a pleonasm.

Breakdown by chemical and mineralogical composition

Tuffs can also be designated by appropriate additives according to their mineralogical and chemical composition. Tuffs or ignimbrites, the chemical and mineralogical correspond to a rhyolite, can be described as rhyolitic tuff or rhyolitic ignimbrites accordingly. Similarly, terms such as basaltic, andesitic and dacitic tuffs can be formed. As an alternative to this example can also tuffs of basaltic, andesitic or dazitischer composition are spoken.

Breakdown by origin

Tuff from pyroclastic fall deposits and pyroclastic flow deposits from tuffs often differ very much from each other, especially in density, hardness, and thus the workability. This is mainly due to the very different temperature of pyroclastic deposits and pyroclastic flow deposits case; pyroclastic flow deposits of the temperature is often very high in contrast to the case of pyroclastic deposits. After deposition of the components contained can be melted partially and on cooling literally be "welded" together. Welded tuff from pyroclastic flow deposits are also Schmelztuffe or ignimbrites (from Latin ignis " fire" imber " rain") called; Ignimbrite is therefore only a special formation of a tuff. Ignimbrites are usually made very compact, often very thick layers, which correspond to one or even several in quick succession following current events. With the naked eye Schmelztuffe or ignimbrites of lava are often difficult to distinguish. Added however is that some authors refer to all deposits of pyroclastic flows, whether fused or solidified normal as ignimbrites.

Scientific Importance

Light up into many kilometers altitude thrown ashes are often drifted thousands of kilometers and can contribute to the deposition of Aschentuffen (or Aschentuffiten ) lead in areas that are far away from the eruption center. Tuffs and tuffites are easily recognizable in drill cores and are suitable for relative and absolute dating, as well as to correlate profiles.

Economic importance and natural stones

Tuff is generally a relatively soft stone (except ignimbrite ) and can therefore be easily processed than natural stone. Due to its ( by gas inclusions caused ) absorbing capacity, he is often used as a building material. Especially in the area around Rome and Naples, where the so-called peperine was already used in ancient times as a building material, can still find many buildings that were built from this tuff.

In Germany tuffs were installed in the building industry as a solid building blocks not only locally, for example, the tuffs from the Eifel are used due to their proximity to the Rhine along the waterways. Examples of this are the Town Hall in Koblenz, Cologne Cathedral and numerous houses in Koblenz.

Thus, the building of the St. Nicolai church in Schleswig-Holstein Hollingstedt of tufa, which was brought from the Eifel region on the Rhine, North Sea, Eider and Treene after Hollingstedt. From there, the Tuff came on to Denmark.

Today tuffs are installed as cladding panels and window sills, rustic stones and regionally Tuffziegel especially outdoors. You have in heritage conservation importance and they are processed by sculptors sculptures. A peculiarity in the use represents the Riedener tuff, tuff because this was mainly used in furnace construction because of its heat storage.

From a Tuffvorkommen at Kruft in the Eifel Trassbindemittel and Trassmörtel for natural stone installation, restoration and other uses in the garden and road are also produced.

Here are some examples:

• Weiberner Tuff ( women, Eifel)
• Ettringer Tuff ( Ettringen, Eifel )
• Riedener Tuff ( vineyards, Eifel )
• Tufo Giallo (Viterbo, Lazio, Italy)
• Rochlitzer porphyry ( Rochlitz, Saxony )
• Hilbersdorfer porphyry (Chemnitz, Saxony )

In Cappadocia came in mighty tuff layers numerous settlements that have been driven into the tuff.

Rock of the Year

The Professional Association of German Geoscientists eV and the German Society for Geosciences have determined the tufa rock for the year 2011. The rationale for the choice is particularly emphasized that tuffs are not only scientifically interesting. Have by use as cement or as a building stone for building and had tuffs of great importance for the history of architecture in Germany.