from Wikipedia, the free encyclopedia
Pending Lower Devonian slate in the northern Eifel. The weathering makes the thin-layer cleavage clearly visible.
Pending Proterozoic mica schist with Sigmaklast of granite (center), Southern Black Hills , South Dakota, United States.
View of the layers of a Jurassic black clay stone, the so-called Posidonia slate , with impressions of fossil shells. Location Holzmaden (width of the handpiece about 11 cm).

Schiefer ( ahd. Scivaro ; mhd. Schiver (e) , stone splinters', 'wood splinters'; mnd. Schiver ,' slate ',' shingle ') is a collective term for different tectonically deformed ( folded ) and sometimes also metamorphic sedimentary rocks . Their common feature is the excellent cleavage along engständiger parallel surfaces, so-called foliation surfaces that are secondarily caused by the deformation. However, undeformed, mostly fine-grained sedimentary rocks that have such fissile properties are traditionally referred to as "slate". However, these rocks split along their primary strata . From this more inclusive traditional name derive e.g. B. the terms oil shale or shale gas , which in the strict petrographic sense stand for a carbon-rich claystone or natural gas still enclosed in its parent rock (usually such a carbon-rich claystone).

In modern petrography, “slate” is only used for tectonically stressed rocks. The traditional name has remained in the scientific literature to this day, mostly in the form of lithostratigraphic names, such as Posidonia slate or copper slate .

Slate species

Undeformed "slate"

Tectonically uncontaminated, very fine-grain sedimentary rocks (English shale ) with high proportions of clay minerals were given the name “slate” well into the 20th century when they split into thin plates. Today, depending on the exact composition, they are called mudstone , siltstone or marl from a petrographic point of view . Oil shales, which are rich in organic material , are actually not slates in the petrographic sense. Nevertheless, this term is still used often today.

The traditional rock names of many of these "false slates" have survived in the form of lithostratigraphic names in geological literature to this day. These include, for example, the fish slate in the Lower Oligocene of the Molasse Basin and in the Aptium of north-west Germany, the Posidonia slate in the Toarcium of southern Germany and the copper slate of the Zechstein series ( Upper Permian ), which is widespread in the underground of Central Europe .

Slate in the modern petrographic sense


SEM images of slate from the southern Urals .
Above: Foliation running from top right to bottom left. The cleavage surfaces are approx. 15 μm apart , with domains with clay minerals in between, which still have the sedimentary layer structure.
Below: The clay minerals are aligned almost completely parallel, the rock was in the area of ​​weak metamorphosis.

Slate (engl. Slate ) are rocks from the transition area from the diagenesis to metamorphosis . There are dense, fine clastic rocks with black, blackish gray, bluish gray, and greenish, yellowish, red and violet color with a engständigen foliation , through the rock in the millimeter range is cleavable.

They arise from claystone under directed pressure and elevated temperatures and can be assigned to both sedimentary and metamorphic rocks . The rock does not yet show any of the typical minerals formed by metamorphosis . During ore formation , the claystone layers are folded in the course of compressing the earth's crust. During these tectonic processes, clay mineral grains are initially released from pressure in the plane parallel to the direction of compression. More or less simultaneously, new clay minerals crystallize in the plane perpendicular to the direction of compression. This gives the original claystone its slate structure .

Pending lower carbon band slate in the Upper Harz

If the foliation is more or less perpendicular to the original stratification, the original stratification can be recognizable as stripes on the foliation surfaces. Such slates are also known as band slates .

The density fluctuates around 2.8 g / cm³. The composition can only be determined by X-ray diffraction , as the diameter of the individual mineral grains is well below 20 μm . The rock consists of larger or smaller amounts of clastic material which, in addition to the actual clay minerals, also contains quartz and feldspar grains as well as detritic mica and chlorite flakes . Slate can also contain tiny amounts of heavy minerals such as dark, needle-shaped rutile crystals or small pyrite cubes . Fossils can often be found in the fine-grained rocks, but they were often distorted or destroyed by the deformation. This does not affect microfossils that can be used to date the rocks.

The affiliation to the group of sedimentary rocks or metamorphic rocks is also determined with the help of X-ray diffraction. In particular, the behavior of the clay mineral illite , which is temperature-sensitive in geological periods, is used, the 10 Å reflection of which is more pronounced with increasing metamorphosis.

Crystalline slate

Geologically , these slates (English schist ) are metamorphic rocks (e.g. green slate , mica slate , glaucoma slate ), in which new sheet silicates such as muscovite , biotite and chlorite have formed from clay minerals under relatively high temperatures and above all high pressure . The mineral “grains” grew in the plane oriented perpendicular to the applied pressure. Therefore, they are all aligned parallel to each other, which makes the rock so easy to split. The formation of the typical structure of crystalline slate is called crystal loblastesis .

Certain minerals such as glaucophane or the minerals of the garnet and amphibole group allow conclusions to be drawn about the pressure-temperature conditions of the metamorphosis . The level of foliation perpendicular to the pressure direction of the metamorphosis has nothing to do with the original sedimentary stratification. The plane of foliation and stratification can be at any angle to one another.

Slate as stone (roof and facade slate)

Black and white slate on a timber frame house in Obercunnersdorf

Roofs and gables and facades are traditionally covered with dark slate . On the Moselle , in the Hunsrück and in the Eifel , building houses with hewn, compact quarry stones made of slate was and is now common again.

Slates and pencils were made from slate from the Middle Ages to the middle of the 20th century . Until the introduction of large-scale industrial paper production and the associated drop in the price of writing paper, slates and pens were a widespread writing material for everyday use, which was indispensable in trade, in private households, but especially in the elementary school education sector, which has been increasing since the 17th century. From the end of the 19th century to the cessation of industrial style slate production in the 1960s, the Thuringian city ​​of Steinach had a world monopoly .

Mining technology

Slate quarry in Lehesten, Thuringia (1948)
Historic roofing slate mine Grube Hoffnung in the Hunsrück
Entrance to an old slate mine tunnel, Grube Vogelsberg 1 in the Hunsrück.
Slate roof

Today's dismantling is determined by the use of modern equipment and machines. The fully mechanized, sawing extraction not only facilitates the work of the miners , but also contributes to the careful handling of the valuable rock .

The minable slate is cut in a grid with a diamond saw along the geological conditions. Block by block, the slate is then removed from the mountain. Wheel loaders take care of the loading underground. The slate is then transported on wagons by mining train to the shaft and from there over the surface to the production halls. Here the slate blocks are sawed, split and trimmed.

In surface production, a diamond saw does the first processing. It ensures that the blocks of different sizes can be used largely "without waste" to manufacture the capstones.

With all mechanization , the shaping processes, the splitting and dressing, are still carried out by hand. The blocks are divided into panels about 5 millimeters thick.

In the Wadrill roof slate pit in Saarland , which was operated until 1953, the slate blocks had to be extracted through the steep to vertical storage (60 ° -90 °) in the ridge construction. In the extraction chambers, the slate blocks were wedged off from bottom to top by notches or by a gentle, pushing extraction shot with black powder. Minable blocks were created underground through the splitting parallel to the foliation (cracking) or the splitting perpendicular to the foliage (heads).

Slate from Germany

In the interest of an orderly competition that is equally transparent for roofers , architects, dealers and builders, the slate extraction sites with somewhat comparable properties from one region were grouped under one name.

As with the well-known vineyard locations, the designation of origin became an indication of properties and quality at the same time. The names and assignments of the pits were determined after long negotiations between the imperial roofing trade and the German slate industry in the early 1920s. The result was published in the official part of the magazine "Das Deutsche Dachdeckerhandwerk" on August 7, 1932. The provisions were reaffirmed in 1953 and 1967 and used by the shale companies today: Moselschiefer , Thuringian Slate , Hunsrücker slate and Sauerland slate .

Accordingly, only the slate from the districts of Mayen, Polch, Müllenbach, Trier and the surrounding area may be called Moselle slate . Nowadays, only the Katzenberg and Margareta mines in Mayen are called Moselle slate. The name comes from the historical transport route of this slate across the Moselle to the Lower Rhine and the Benelux countries. The designation Hunsrücker Schiefer applies to the districts Altlay, Bundenbach, Kirn, Gemünden and Herrstein and their surroundings . The extraction sites in Fredeburg, Brilon, Nuttlar etc. fall under the generic term slate from Westphalia and Waldeck , but are also simply called Sauerland slate , although, as in other regions, there can be significant differences in properties within this designation.

Are still in production today

  • in the Hochsauerland in the area around Bad Fredeburg a composite mine with the pits Bierkeller, Gomer, Magog with a 150-year tradition,
  • in the Hunsrück the Altlay slate mine (with an underground extraction at a depth of around 120 meters under centuries-old quarries). For 2020, the operator of the Altlay mine announced the start of slate mining in open-cast mining in "new, untouched slate storage facilities".
  • in Bavaria near (municipality of Geroldsgrün ) (after a 500 meter long conveyor tunnel) the Lotharheiler slate .

The Moselle slate mining around Mayen was traditionally the most powerful German location with over half of the German production. The largest known occurrence of roofing slate is, however, in the area around Bad Fredeburg.

Penrhyn Quarry near Bethesda, Wales, circa 1890
Slate mining in Spain

Slate was also mined in Thuringia until 2008, with a mine in Unterloquitz and an open-cast mine near Schmiedebach in operation. From the Middle Ages to the second half of the 20th century in the Harz, especially south of Goslar, the so-called Wissenbach slate was extracted as roof slate in mines and quarries, including in the Glockenberg mine . In Kaub on the Middle Rhine , roofing slate of the highest quality was extracted for centuries until 1972. The day-to-day facilities of the Wilhelm Erbstollen mine still bear witness to the former importance of slate mining for the entire region.

Other mining countries

Slate is found in many countries around the world: also outside of Europe in North America, in South America, South Africa, Japan, China, Russia (Siberia) and India. In Europe, slate deposits occur in Slovenia, Croatia, Greece, Italy, the Czech Republic, Poland, Hungary, Norway, Sweden, Switzerland, Portugal, Spain, France, Belgium, Luxembourg , Great Britain and Ireland.

Significant productions in terms of volume can be found - in that order - in Spain, France, Great Britain, Germany and Portugal. The largest consumer country, however, is by far France. This traditional “slate country” has what used to be a significant national production (Ardoisières d'Angers), but is also the largest buyer of Spanish slate. Traditional “slate countries” in terms of use are also Germany, Benelux and Great Britain.



There are slate museums among others:

foreign countries

See also

Web links

Commons : Slate  - collection of pictures, videos and audio files
Wiktionary: Slate  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ^ Walter Maresch, Karl Medenbach: Rocks . Mosaik Verlag, Munich 1987, ISBN 3-576-10699-5 , pp. 202 .
  2. Holger Maurer: Reconstruction of the deposit conditions in the North Alpine foreland basin in Southwest Germany. Dissertation approved by the Faculty of Geosciences and Biosciences at the University of Stuttgart to obtain the title of Doctor of Natural Sciences. Stuttgart 2006, urn : nbn: de: bsz: 93-opus-30205 , p. 34.
  3. German Stratigraphic Commission (Ed.): Stratigraphische Tisch von Deutschland 2002 . Potsdam 2002, ISBN 3-00-010197-7 .
  4. ^ Walter Maresch, Karl Medenbach: Rocks . Mosaik Verlag, Munich 1987, ISBN 3-576-10699-5 , pp. 162 and 210 .
  5. Werner Pleßmann: Rock solution, a main factor in the foliation process . In: Geological communications . tape 4 . Aachen 1964, DNB  012615323 , p. 69-82 .
  6. Wolfhard Wimmernauer: Petrography of igneous and metamorphic rocks . Enke, Stuttgart 1985, ISBN 3-432-94671-6 , pp. 295 f .
  7. Hanan J. Kisch: Illite crystallinity: recommendations on sample preparation, X-ray diffraction settings, and interlaboratory samples . In: Journal of Metamorphic Geology . Volume 9, No. 6 , 1991, pp. 665-670 , doi : 10.1111 / j.1525-1314.1991.tb00556.x .
  8. ^ History. In: Theis-Böger company's website. Retrieved November 13, 2019 .
  9. ^ The Slate Industry of North and Mid Wales
  10. Heinz-Gerd Röhling, Friedhart Knolle: Also on the town hall of Wernigerode ... - Slate and its extraction in the UNESCO Geopark Harz - Braunschweiger Land - Ostfalen. New Wernigeröder newspaper. 29th vol., No. 23–25, 2018, pp. 48–50 ( ResearchGate )
  11. ^ Slate exhibition mine Raumland official website
  12. Slate building Nuttlar UG - the adventure mine
  13. Thuringian Slate Mountains Nature Park / Upper Saale
  14. ^ Information on the Trélazé municipality website
  16. ^ Homepage region , homepage museum