Jurassic marble
Jura marble , also called Jura or Jura limestone or Jura limestone , is the trade name of a light yellow to blue - gray fossil - rich limestone from the upper White Jura of the Franconian Alb in the Eichstätt , Treuchtlingen and Petersbuch - Erkertshofen area . In addition to Treuchtlingen, earlier Jura marble mining areas were also near Pappenheim - this is why it is also called Treuchtlinger marble . Today (2010) this natural stone is used extensively in the Titting andKaldorf dismantled.
The Jura marble quarrying area is likely to be the largest active quarrying area for natural stone in Germany.
geology
The name Jura marble is a trade name whose part of the name marble is incorrect from a petrographic (rock science) point of view. Petro Graphically it is a fossil -rich limestone (more precisely, "a bioclasts -rich tuberolithischen sponge Biostrom lime") with fine-grained matrix . In the natural stone trade, all carbonate stones that can be polished with clover salt are called “marbles”. However, the designation Jura limestone is also ambiguous from a geological point of view, as it can stand for any limestone that was formed in the Jura era . In geological literature, natural stone is often referred to as “Treuchtlinger marble” (with or without quotation marks).
Lithostratigraphically the average of 1 m constitute powerful banks of the Jura marble (Local term "color layers") together with the marl layers through which they are separated, the Petersbuch-Subformation the Treuchtlingen formation of the Jurassic the Frankish Alb. Their age can therefore be set at approx. 155 million years ( Kimmeridgian , Upper Jurassic ). The thickness of the usable deposit within the White Jura is approx. 50 m.
Common fossils that are visible to the naked eye (macroscopically) are silica sponges , ammonites and belemnites . Also striking are mass occurrences of systematically uncertain classifiable micro fossil Tubiphytes (or Crescentiella ) morronensis who speak out on polished gates in the form of darker, "cloudy" areas with characteristic white mottling. The dense matrix of the rock was created by microorganisms (hence called microbialith), but probably not mainly, as it is sometimes suggested in the literature, by colonies of unicellular algae and / or cyanobacteria ("blue-green algae"). Although the matrix has a partly thrombolithic , partly stromatolithic microstructure, which is typical of the calcareous crusts of (blue) algae mats, it must be assumed on the basis of palaeological considerations that the Jura marble, among other things because of the clear dominance of sponges over reef-building corals , in relatively deep water, below at least 50 meters, in poor light conditions. The evidence of so-called cryptic microbialites, i.e. H. Under poor light conditions in caverns of recent coral reefs microbially formed calcareous crusts, with very similar microstructure and isotope composition ( δ 18 O , δ 13 C ) supports this thesis. The grayish variants of the Jura marble contain pyrite , partly in the form of macroscopically visible, typically shiny gold inclusions - in the yellowish variants the pyrite is oxidized to " limonite ".
The Jura marble is not to be confused with the Solnhofen limestone , which is geologically only a little younger and geographically widespread in the same region. Solnhofen is a cleavable into thin sheets, very fine-grained limestone, which for its detailed obtained fossils - especially by vertebrate fossils and "Urvogel" Archeopteryx - and its suitability as a printing plate in the lithography is known (lithography). Jurassic marble was created under different environmental conditions and therefore has a different composition of fossil fauna and preservation and cannot be split into thin slabs.
In addition, two other Upper Jurassic carbonate rocks are being quarried along the Altmühl in the southern Franconian Alb area, which have also been used as stone in architecture for a long time : Wachenzeller dolomite and Kelheim limestone .
Jurassic marble as a cultural asset
Jurassic marble has been used as a building material since the beginning of human settlement . The rock, which can be easily extracted for the construction of castles and houses of the upper class, led to the establishment of settlements near the quarries.
Stone was rarely used to decorate interiors. Only the technique of polishing the surfaces with clover salt led to the increased use of Jurassic lime in sacred buildings for columns or altars.
Historical and modern sculptors created sculptures and in particular in the Eichstätter Dom there are historical sculptures and designed stones of European standing.
- Works made from Jurassic limestone from Eichstätter Dom
Late baroque west facade of the cathedral
Life-size statue of St. Willibald von Loy Hering
Pappenheim altar of the early Renaissance with a total height of 11 meters
The "beautiful pillar" in the mortuary of the cathedral
Mining and economic history
It is assumed that the first large-scale quarrying of Jura marble took place during the construction of Willibaldsburg (1351-1365). At the end of the 18th century, quarries in the city were marked on maps of Eichstätt. The first evidence of a quarry operation can be found in a contract between Leo von Klenze and the Eichstätter quarry owner and master stonemason Anton Wagner for the construction of the Regensburg Walhalla from 1825.
When Treuchtlinger Marmorwerke AG was founded in 1911, the industrial mining of Jura marble for bridges, monuments, feed troughs, fence posts and paving stones began. The global economic crisis of 1929 also affected the stone industry with falling sales and the layoff of workers. An upswing followed by 1939 with deliveries for monumental buildings of the National Socialists , such as the buildings on the Nuremberg Nazi party rally grounds . After interruptions during the Second World War , companies that previously mainly processed Solnhofen limestone also began to quarry Jura marble. The quarry areas in Petersbuch-Erkersthofen were developed in the mid-1950s and later those in the municipality of Titting.
The first post-war recession in Germany in 1966/1967 led to a decline in sales of natural stone. In the subsequent construction boom towards the end of the 1960s, the stone processing companies in the Jura region prospered again. From the mid-1970s, however, they were increasingly in competition with the Italian stone industry, which was successful with marble on the German market. The collapse of the socialist camp and its use for major projects in Arab countries, especially in Saudi Arabia , resulted in an upswing again in the 1990s. In the course of the globalized economy, there was increased competition from India and China, which again led to economic problems for stone processing companies, especially due to the decline in export demand from 2008 onwards.
Appearance
The best known variant of Jura marble is Jura yellow (also banded in the variant ). The yellow color is due to the limonite content . The second most common variant is Jura gray ( gray-blue ). Jura-Bunt ( mixed gray-yellow ) comes from the interfaces of rock banks of the gray and yellow varieties. Rarer colors are red brown, Jura nut brown , a more brownish variant, and Jura cream white , which is obtained from a light yellow zone. Jurassic travertine is created by sawing the rock against the bearing and then showing a structure that is similar to travertine .
Occasionally, alleged "cracks" are criticized, but they consist of natural, transparent calcite veins and do not represent a technical defect. As with many other organo-limes , a 100% homogeneous polish is not possible.
Properties and use
With a hardness of 3 to 3.5 on the Mohs scale (1 - 10), the Jura marble and the Solnhofen limestone are soft rocks. Nevertheless, the density is high, resulting in good polishability.
The average density is 2.5 kg / dm³, the compressive strength is 125 N / mm², the flexural strength is 11.5 N / mm², the water absorption is 1.8% by weight, the abrasion resistance according to DIN EN 14157 / B Böhme at 18 cm³ / 50 cm² or according to Capon at 20 mm and the thermal conductivity λ at 2.3 W / mk.
Jurassic marble is used extensively as stone in the interior and occasionally on the facade. Floor panels are usually manufactured with a side length of up to 100 cm, window sills up to 300 cm. The panel thickness is usually between 10 and 50 mm. The surface is offered as diamond-sawn, ground, polished, bush-hammered, bush-hammered, sand-blasted, grooved or "antique".
Indoor areas
In addition to brickwork, masonry and building blocks, Jura marble was also used in manorial houses for the decorative interior design of clerical and profane buildings. Veneers, vanities, banisters and sculptures were made from it.
The manufacture of floor and stair coverings was laborious in pre-industrial times. The broken plates were roughly machined and then sanded by hand with an iron block and fine sand . Finally, it was either polished or the floor was "deeply" embedded with soft soap .
With the start of the industrial revolution, machine-worked window sills, flooring and wall coverings began to be produced on a large scale. Jura marble has been a typical window sill material since the post-war period.
The Jura marble, which is somewhat out of fashion in Germany, has become more popular abroad due to its warm, neutral look and the occasional fossils it contains.
Jura marble is usually well suited for underfloor heating , as it is homogeneous and only small proportions of clayey layers occur at the boundaries of the individual rock layers.
Outdoor areas
Not every fracture layer of Jura marble is suitable for outdoor use. As with most limestone, a polished surface loses its sheen when exposed to weather .
If Jura marble is used outside, no layer-forming seals ( stone seals ), nano-coatings or impregnations can be used, as these interrupt the capillary conductivity, reduce the vapor diffusion resistance and thereby impair frost resistance. Specialist companies often refuse to accept liability if unsuitable coatings are applied. Flaking does not occur immediately, but usually only after three to five years.
(Stone) soap, on the other hand, has a patinating effect without the disadvantages mentioned above. A layer of lime soap forms , which hardly reduces the vapor permeability.
Floor coverings
Jura yellow is only partially frost-resistant. A reliably draining substructure is therefore important . Terrace tiles that are laid in gravel or facade tiles that are freely suspended from anchors do not freeze. When laying in the mortar bed , flaking can occur at the interface with the mortar. The reason for this is the alkalinity of the mortar, which breaks the (albeit small) iron bond at the interface. It should be noted that when determining the frost resistance in accordance with DIN EN 1341-44, only the rock, but not the entire structure, is tested.
Solid components in gardening and landscaping
Solid components are often made from Jura Yellow. Today often in the form of crust plates .
Block steps and paving slabs have been used around Eichstätt for centuries . Numerous castles, palaces, churches and other structures were built from massive stone made of Jura marble and defy weathering , with the material thickness playing a decisive role.
cleaning
Limestone, especially Jura marble, is sensitive to acidic cleaning agents such as vinegar and toilet cleaners, as the acid it contains dissolves lime. Highly alkaline products, such as professional deep cleaners based on caustic soda or potassium hydroxide, are also generally not recommended because they can attack the components of the fossils stored in the stone . Solvents such as petrol or turpentine can lighten the stone if the stone has previously been treated with tinting or patinating agents.
The cement film removers often used after laying tiles and granite slabs are acidic and therefore not suitable for Jura marble. Alkaline ammonia- based cleaning agents (pH 7-10.5) can be used to remove heavy soiling . The floor covering must be pre-moistened with water until it is saturated. Remove excess water with a rubber squeegee. The cleaning solution can then be used to scrub the stones on the floor. Brush again after approx. 5 minutes. Then rinse at least twice with clear water.
Limestone was already tended with soap by the Sumerians . As a result, so-called lime soaps build up, which result in a silk-matt and color-intensive look and cause a certain patina to develop over time . The resulting soap layer provides a certain protection against deposits and some soiling, but cannot prevent stains from oils, fats and discoloration from red wine and other coloring liquids.
If necessary, the natural stone can be polished with a satin finishing or brushing machine. An efficient and thorough cleaning is carried out with a scrub-suction machine with a "high-low brush" with bristles of 0.3 and 0.5 mm. Pads are not recommended.
See also
Guidelines
The laying of sheet material is carried out in accordance with DIN 18332, DIN EN 1469, EN 12057 and 12058 (also over underfloor heating). The Industrieverband Altmühltaler Kalksteine e. V. publishes installation and maintenance instructions.
Web links
- Jura marble - mining, processing and sales on baufachinformation.de
- A heart made of stone - How the Jura marble shapes the landscape
Individual evidence
- ^ Friedrich Müller: INSK compact. The current natural stone index for the current market. Pages 69.1 and 67.5. Ebner Verlag Ulm. 1st edition 1997.
- ↑ a b Birgit Niebuhr, Thomas Pürner: Plattenkalk and Frankendolomit - lithostratigraphy of the Weißjura group of the Franconian Jura (Upper Jura, Bavaria). Publication series of the German Society for Geosciences, No. 83.Swisserbart (on commission), Hanover 2014, ISBN 978-3-510-49232-9 ( abstract )
- ^ German Stratigraphic Commission (Ed .; coordination and design: Manfred Menning, Andreas Hendrich): Stratigraphic Table of Germany 2016. Deutsches GeoForschungsZentrum, Potsdam 2016, ISBN 978-3-9816597-7-1 ( online )
- ↑ Baba Senowbari-Daryan, Ioan I. Bucur, Felix Schlagintweit, Emanoil Săsăran, Jacek Matyszkiewicz: Crescentiella , a new name for “ Tubiphytes ” morronensis CRESCENTI, 1969: an enigmatic Jurassic - Cretaceous microfossil. Geologia Croatica. Vol. 61, No. 2-3, 2008, pp. 185-214, ( online ); Note: In this work, reference to southern German deposits is sometimes referred to as "Plattenkalk" (e.g. in the caption to Fig. 1), but the information in the section "Material and Methods" (p. 186) is relative clearly shows that only samples from "Treuchtlinger marble" were examined from Germany.
- ↑ a b c Helmut Keupp, Angela Jenisch, Regina Herrmann, Fritz Neuweiler, Joachim Reitner: Microbial Carbonate Crusts - a Key to the Environmental Analysis of Fossil Spongiolites? Facies. Vol. 29, No. 1, 1993, pp. 21-54, doi: 10.1007 / BF02536916 (alternative full text access : GoeScholar ); see also literature cited therein.
- ↑ The economic history of Solnhofen slabs and Jura marble on solnhofen-fossilienatlas.de . Retrieved July 17, 2010
- ↑ a b c Jura marble - technical data , Industrievereinigung Altmühltaler Kalksteine eV
- ↑ Herbert Fahrenkrog: Natural stone in everyday life. Questions & Answers . In: Magna Newsletter complete, pp. 84–89. 1st edition 2007. Edited by Magna. Callwey Verlag Munich, o.A.
- ^ Treatment of Jurassic limestone . Leaflet 48. Ed. by Lithofin, accessed on December 15, 2014
- ↑ Juramarmor , Industrievereinigung Altmühltaler Kalksteine eV