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93-574: Lehesten is a town in the Thuringian Forest , 20 km southeast of Saalfeld . After an August 1944 explosion at the Redl-Zipf V-2 liquid oxygen plant at Schlier stopped production, the third V-2 liquid oxygen plant (5000 tons/month) was built at a slate quarry at Lehesten at the Thuringia-Bavarian border near Nordhausen (acceptance testing of combustion chamber was also performed at

186-709: A barrier to the main weather currents, erosion is strong and has led to a more pronounced relief than in many other of the European low mountain chains. The mean temperatures decrease with altitude: While the Thuringian Basin experiences less than 100 days per year with temperatures below 0 °C, this number rises to more than 150 in the upper altitudes of the Thuringian Forest. The Northwest Thuringian Forest comprises an area of about 70 km reaching heights up to 470 m (1,540 ft), hardly exceeding those of

279-408: A distinctive composition or mode or origin. Special names still in wide use include amphibolite, greenschist , phyllite, marble, serpentinite , eclogite, migmatite , skarn , granulite , mylonite, and slate. The basic classification can be supplemented by terms describing mineral content or texture. For example, a metabasalt showing weak schistosity might be described as a gneissic metabasalt, and

372-451: A distinctive layering called foliation (derived from the Latin word folia , meaning "leaves"). Foliation develops when a rock is being shortened along one axis during recrystallization. This causes crystals of platy minerals, such as mica and chlorite , to become rotated such that their short axes are parallel to the direction of shortening. This results in a banded, or foliated, rock, with

465-464: A marble will not be identical with the amphibolite facies of a pelite. However, the facies are defined such that metamorphic rock with as broad a range of compositions as is practical can be assigned to a particular facies. The present definition of metamorphic facies is largely based on the work of the Finnish geologist, Pentti Eskola , with refinements based on subsequent experimental work. Eskola drew upon

558-522: A metamorphic rock to be classified in this manner, the protolith should be identifiable from the characteristics of the metamorphic rock itself, and not inferred from other information. Under the British Geological Survey's classification system, if all that can be determined about the protolith is its general type, such as sedimentary or volcanic, the classification is based on the mineral mode (the volume percentages of different minerals in

651-568: A part of the Thuringian Basin , but with numerous deeply eroded river valleys and the dense forestation they resemble very much the Thuringian Forest. The Thuringian Forest is located in the Central European transition zone between the Atlantic oceanic climate and the continental climate of Eastern Europe. Humid air arrives mainly from the west, so that the western slopes and the crest of

744-413: A pelite containing abundant staurolite might be described as a staurolite pelite. [REDACTED] A metamorphic facies is a set of distinctive assemblages of minerals that are found in metamorphic rock that formed under a specific combination of pressure and temperature. The particular assemblage is somewhat dependent on the composition of that protolith, so that (for example) the amphibolite facies of

837-519: A relatively mild grade of metamorphism, at temperatures of 350–500 °C (662–932 °F) and pressures of 200–500 MPa (2,000–5,000 bar). They can be divided into a lower group of metabasalts, including rare meta komatiites ; a middle group of meta-intermediate-rock and meta-felsic-rock; and an upper group of metasedimentary rock. The greenstone belts are surrounded by high-grade gneiss terrains showing highly deformed low-pressure, high-temperature (over 500 °C (932 °F)) metamorphism to

930-515: A separate structure, is geologically very similar to the latter, as it consists of the same rock types such as granite, hornfels , porphyrites, Rotliegend and Zechstein sediments, and thus forms part of the Variscan chain. It is about 11 km (6.8 mi) long and 1 km (0.62 mi) to 2 km (1.2 mi) wide, with an average altitude of 460 m. Mining for fluorite , baryte , and limonite has been attempted there on several occasions, but

1023-552: A stream from Albrechts, feeding into the Werra . This region between federal roads B 4 between Ilmenau and Stützerbach , following the rivers Ilm , Lengwitz, and Nahe, and B 247 between Luisenthal and Suhl contains the three highest summits as well as the fifth highest summit of the whole range. The only settlements wholly within this region are Gehlberg north of Rennsteig and Vesser south of it. Parts of Schmiedefeld and Goldlauter-Heidersbach (part of Suhl) also extend into this part of

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1116-410: A variety of metamorphic facies. Where subduction is taking place, the basalt of the subducting slab is metamorphosed to high-pressure metamorphic facies. It initially undergoes low-grade metamorphism to metabasalt of the zeolite and prehnite-pumpellyite facies , but as the basalt subducts to greater depths, it is metamorphosed to the blueschist facies and then the eclogite facies . Metamorphism to

1209-407: Is Großer Beerberg at 982 m (3,222 ft) above sea level. The Rennsteig (sometimes called Rennweg ) is an ancient path following the main ridge and connecting the summits. It is now a famous hiking path and marks the traditional boundary between the hills -dominated terrain of central Germany and the more rugged terrain characteristic of southern Germany, and also the boundary between

1302-417: Is a great variety of metamorphic rock types. In general, if the protolith of a metamorphic rock can be determined, the rock is described by adding the prefix meta- to the protolith rock name. For example, if the protolith is known to be basalt , the rock will be described as a metabasalt. Likewise, a metamorphic rock whose protolith is known to be a conglomerate will be described as a metaconglomerate . For

1395-426: Is called a paired metamorphic belt . The main islands of Japan show three distinct paired metamorphic belts, corresponding to different episodes of subduction. Metamorphic rock is also exposed in metamorphic core complexes , which form in region of crustal extension. They are characterized by low-angle faulting that exposes domes of middle or lower crust metamorphic rock. These were first recognized and studied in

1488-511: Is dominated by metamorphic rock that has reached the amphibolite facies. Within the upper crust, which is the only part of the Earth's crust geologists can directly sample, metamorphic rock forms only from processes that can occur at shallow depth. These are contact (thermal) metamorphism , dynamic (cataclastic) metamorphism , hydrothermal metamorphism , and impact metamorphism . These processes are relatively local in occurrence and usually reach only

1581-536: Is drained towards the north by the river Lütsche which feeds the Lütsche reservoir and by Wilde Gera and Zahme Gera towards Gera river and Unstrut , and by Freibach stream, a tributary of Ilm river, and towards the south by Lauter , a tributary of Hasel, and mainly by Erle , feeding the Erle reservoir, Breitenbach, Vesser, and Nahe into Schleuse . Notable summits include: The region around Frauenwald and Neustadt forms

1674-476: Is formed as tectonic plates move apart. Hydrothermal metamorphism is extensive here. This is characterized by metasomatism by hot fluids circulating through the rock. This produces metamorphic rock of the greenschist facies. The metamorphic rock, serpentinite , is particularly characteristic of these settings, and represents chemical transformation of olivine and pyroxene in ultramafic rock to serpentine group minerals. Contact metamorphism takes place when magma

1767-403: Is injected into the surrounding solid rock ( country rock ). The changes that occur are greatest wherever the magma comes into contact with the rock because the temperatures are highest at this boundary and decrease with distance from it. Around the igneous rock that forms from the cooling magma is a metamorphosed zone called a contact aureole . Aureoles may show all degrees of metamorphism from

1860-405: Is known as burial metamorphism . This tends to produce low-grade metamorphic rock. Much more common is metamorphic rock formed during the collision process itself. The collision of plates causes high temperatures, pressures and deformation in the rocks along these belts. Metamorphic rock formed in these settings tends to shown well-developed schistosity. Metamorphic rock of orogenic belts shows

1953-751: Is known for the so-called Drachenschlucht , a narrow gorge near Eisenach, and the Wartburg castle. The northern part of the area is drained by several streams into the Hörsel , the southern part into the Elte. Hence, the ridge of the Northwestern Thuringian Forest only forms the watershed between Hörsel and the middle course of the Werra . Notable summits include: The much larger natural region of Central Thuringian Forest with an area of about 850 km , whose ridge rises mostly above 600 m (2,000 ft),

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2046-576: Is subdivided into several parts described below in their sequence from the north-west to the south-east. This part, situated around the town of Ruhla north of the Rennsteig , is geologically formed by the basement rocks of the Ruhlaer Kristallin , consisting of granites , gneiss , and schist . There is no pronounced ridge, summits on both sides of the watershed reach heights of 700 m (2,300 ft) or more. Its northeastern parts drain towards

2139-506: Is sufficiently hard and dense that it is difficult to quarry. However, some quartzite is used as dimension stone , often as slabs for flooring, walls, or stairsteps. About 6% of crushed stone, used mostly for road aggregate, is quartzite. Marble is also prized for building construction and as a medium for sculpture. Schistose bedrock can pose a challenge for civil engineering because of its pronounced planes of weakness. A hazard may exist even in undisturbed terrain. On August 17, 1959,

2232-545: Is transformed physically or chemically at elevated temperature, without actually melting to any great degree. The importance of heating in the formation of metamorphic rock was first noted by the pioneering Scottish naturalist, James Hutton , who is often described as the father of modern geology. Hutton wrote in 1795 that some rock beds of the Scottish Highlands had originally been sedimentary rock but had been transformed by great heat. Hutton also speculated that pressure

2325-400: Is uncertain. Special classifications exist for metamorphic rocks with a volcaniclastic protolith or formed along a fault or through hydrothermal circulation . A few special names are used for rocks of unknown protolith but known modal composition, such as marble, eclogite , or amphibolite . Special names may also be applied more generally to rocks dominated by a single mineral, or with

2418-426: Is used only when very little else is known about the rock that would allow a more definite classification. Textural classifications may be prefixed to indicate a sedimentary protolith ( para- , such as paraschist) or igneous protolith ( ortho- , such as orthogneiss). When nothing is known about the protolith, the textural name is used without a prefix. For example, a schist is a rock with schistose texture whose protolith

2511-475: Is usually devoid of schistosity and forms a tough, equigranular rock. If the rock was originally banded or foliated (as, for example, a laminated sandstone or a foliated calc- schist ) this character may not be obliterated, and a banded hornfels is the product. Contact metamorphism close to the surface produces distinctive low-pressure metamorphic minerals, such as spinel , andalusite, vesuvianite , or wollastonite . Similar changes may be induced in shales by

2604-470: Is very low in silica) to metafelsic-rock (with a high silica content). Where the mineral mode cannot be determined, as is often the case when rock is first examined in the field , then classification must be based on texture. The textural types are: A hornfels is a granofels that is known to result from contact metamorphism. A slate is a fine-grained metamorphic rock that easily splits into thin plates but shows no obvious compositional layering. The term

2697-566: The Basin and Range Province of southwestern North America, but are also found in southern Aegean Sea , in the D'Entrecasteaux Islands , and in other areas of extension. Continental shields are regions of exposed ancient rock that make up the stable cores of continents. The rock exposed in the oldest regions of shields, which is of Archean age (over 2500 million years old), mostly belong to granite-greenstone belts. The greenstone belts contain metavolcanic and metasedimentary rock that has undergone

2790-491: The Rennsteig , reaches heights of around 900 m at several places southwest to west of Oberhof, but does not really form any individual mountains and has very much the character of a mountain crest. By contrast, the Großer Hermannsberg and Ruppberg (see below) that rise to the southwest of the ridge are better known and popular tourist destinations. To the northeast, where the terrain gradually flattens out, are two of

2883-841: The Saale . The Apfelstädt is impounded by the Tambach-Dietharz Dam into a small lake and the Schmalwasser and Ohra by the Schmalwasser and Ohra Dams into larger reservoirs. The south is drained by the Asbach which flows via the Stille into the Schmalkalde and by rivers and streams belonging to the fan-like system of tributaries of Hasel (Werra) , in particular the Schwarza , Häselbach , Lichtenau and

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2976-569: The Werra Railway between Eisenach and Eisfeld does so in a tunnel near Förtha . Both are in daily operation. A third line, the southern section of the Plaue–Themar railway, does not use a tunnel, but crosses the mountain ridge at Rennsteig switchback station. It has only been used by museum trains since 1998. The Nuremberg–Erfurt high-speed railway , due to be commissioned in December 2017, crosses

3069-450: The atoms and ions in solid crystals to migrate, thus reorganizing the crystals, while high pressures cause solution of the crystals within the rock at their point of contact. Metamorphic rocks are characterized by their distinctive mineral composition and texture. Because every mineral is stable only within certain limits, the presence of certain minerals in metamorphic rocks indicates the approximate temperatures and pressures at which

3162-402: The crystallization of igneous rocks. They are stable at high temperatures and pressures and may remain chemically unchanged during the metamorphic process. Metamorphic rocks are typically more coarsely crystalline than the protolith from which they formed. Atoms in the interior of a crystal are surrounded by a stable arrangement of neighboring atoms. This is partially missing at the surface of

3255-627: The 3 largest reservoirs in the Thuringian Forest (see below). The best known rock formation in the mountain range, the Falkenstein , is also found in this area. Notable summits include: The northeastern flank of the mountains is drained by right tributaries of the Apfelstädt , especially the Schmalwasser , and left tributaries of the Ohra , notably the Kernwasser, via the (Apfelstädt,) Gera and Unstrut into

3348-689: The Central German Crystalline Zone, of which Odenwald and Spessart are also constituents. In the Rotliegend era the region formed the crest of a mountain range where the debris originated that was deposited in the Eisenach trough and the northwestern part of the Oberhof trough. The sedimentary, volcano-sedimentary, and magmatic rocks which were deposited or formed in the area from the Cambrian until

3441-452: The Earth's surface following erosion and uplift) provides information about the temperatures and pressures that occur at great depths within the Earth's crust. Some examples of metamorphic rocks are gneiss , slate , marble , schist , and quartzite . Slate and quartzite tiles are used in building construction. Marble is also prized for building construction and as a medium for sculpture. On

3534-435: The Earth's surface, where they are subject to high temperatures and the great pressure of the rock layers above. They can also form from tectonic processes such as continental collisions, which cause horizontal pressure, friction, and distortion. Metamorphic rock can be formed locally when rock is heated by the intrusion of hot molten rock called magma from the Earth's interior. The study of metamorphic rocks (now exposed at

3627-705: The Forest. The highest summits crowning the mountain ridge are of volcanic origin. The terrain dips rapidly down to heights below 800 m towards the north-east, while heights remain above this altitude south-west of Rennsteig for some distance in the horseshoe-shaped Adlersberg massif. Motorway A 71 and the Neudietendorf–Ritschenhausen railway pass under the Brandleite Massif between Gehlberg and Oberhof in Rennsteig road tunnel and Brandleite Tunnel . The area

3720-544: The Hörsel, the southwestern parts towards the middle course of the Werra. The area is limited towards the south-east by state road 1027 between Schwarzhausen and Bad Liebenstein. Notable summits include: Reaching until Tambach-Dietharz , the part of Thuringian forest around the town of Brotterode is geologically more heterogeneous than the region around Ruhla. State road 1026 between Friedrichroda and Floh-Seligenthal which follows

3813-512: The Lehesten plant). Dr Martin Schilling (the head of testing at Peenemünde) located the Lehesten site, and 400 engineers were moved from Peenemünde to Lehesten, which eventually had 16 liquid oxygen production plants. This Saalfeld-Rudolstadt location article is a stub . You can help Misplaced Pages by expanding it . Thuringian Forest Among scattered foothills at its northern foot are

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3906-409: The Oberhof trough had been a rift zone with intense tectonics and continual changes of the internal relief and of the main areas of deposition. The tectonic processes were accompanied by an intense felsitic volcanism which was the origin of many volcanic rock formations, predominantly rhyolites of porphyric structure with accompanying tuff deposits. These volcanic rocks alternate in sequence with

3999-454: The Rotliegend era, and the conglomerates, sandstones, and abundant volcanic rocks ( rhyolites and andesites ) of the Oberhof trough. Ore deposits associated with the upthrust of the range have been of significant historical importance in the development of the region, for example, the metalworking tradition in Suhl and the mining history of Ilmenau . The uplift of the horst -like fault block

4092-459: The Thuringian Forest with the help of several tunnels and bridges. Thüringerwaldbahn, a cross-country line of the Gotha tramway network, serves the northern foothills of the Thuringian Forest between Gotha and Bad Tabarz , including a branch to Waltershausen . Geologically, the Thuringian Forest is defined by a belt of strongly uplifted and deformed metamorphic and igneous rock that divides

4185-549: The Thuringian forest. The lack of volcanic rocks suggests that at the time of the deposition of the Eisenach formation, no significant tectonic processes took place in the Werra basin which was by then a mostly consolidated depositional environment. In the Ruhla anticline the basement rocks, folded in the Variscan era, are exposed. They are named Ruhlaer Kristallin after the location and are according to Franz Kossmat considered part of

4278-640: The Vesser complex near Schmiedefeld , an island of Variscan rocks embedded in Rotliegend. While the near-surface rocks of the Thuringian Highland comprise mostly the folded Variscan basement , the oldest unfolded overlying strata (dating from the Permosilesian age) of this basement are exposed in the Thuringian forest. Common to both ranges, but also to other low mountain ranges in Central Europe uplifted at

4371-447: The adjacent Buntsandstein forelands to the southwest, but exhibiting a much more pronounced relief. It stretches until Moosbach stream, a tributary or Erbstrom river, in the north east, and to Bundesstraße 19 in the east and south, which follows the upper reaches of Elte river between the villages of Wilhelmsthal and Etterwinden. The predominant rock species is Eisenacher Rotliegend , namely conglomerates and sandstones . The area

4464-477: The amphibolite or granulite facies. These form most of the exposed rock in Archean cratons. The granite-greenstone belts are intruded by a distinctive group of granitic rocks called the tonalite - trondhjemite - granodiorite or TTG suite. These are the most voluminous rocks in the craton and may represent an important early phase in the formation of continental crust. Mid-ocean ridges are where new oceanic crust

4557-404: The bands showing the colors of the minerals that formed them. Foliated rock often develops planes of cleavage . Slate is an example of a foliated metamorphic rock, originating from shale , and it typically shows well-developed cleavage that allows slate to be split into thin plates. The type of foliation that develops depends on the metamorphic grade. For instance, starting with a mudstone ,

4650-420: The bulk composition of a rock. Hot fluids circulating through pore space in the rock can dissolve existing minerals and precipitate new minerals. Dissolved substances are transported out of the rock by the fluids while new substances are brought in by fresh fluids. This can obviously change the mineral makeup of the rock. However, changes in the mineral composition can take place even when the bulk composition of

4743-399: The burning of coal seams. This produces a rock type named clinker . There is also a tendency for metasomatism between the igneous magma and sedimentary country rock, whereby the chemicals in each are exchanged or introduced into the other. In that case, hybrid rocks called skarn arise. Dynamic (cataclastic) metamorphism takes place locally along faults . Here intense shearing of

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4836-475: The chain experience the highest levels of precipitation. While the exception of the northwestern part with its lower altitudes (650 mm), the yearly precipitation reaches about 1000 mm, in the higher parts up to about 1300 mm. In contrast, the leeward Thuringian Basin is one of the driest regions in Germany with only around 460 mm to 590 mm of precipitation per year. As the Thuringian Forest forms

4929-435: The circulation of fluids through buried rock, to the list of processes that help bring about metamorphism. However, metamorphism can take place without metasomatism ( isochemical metamorphism ) or at depths of just a few hundred meters where pressures are relatively low (for example, in contact metamorphism ). Metamorphic processes change the texture or mineral composition of the metamorphosed rock. Metasomatism can change

5022-427: The collision of tectonic plates at convergent boundaries . Here formerly deeply buried rock has been brought to the surface by uplift and erosion. The metamorphic rock exposed in orogenic belts may have been metamorphosed simply by being at great depths below the Earth's surface, subjected to high temperatures and the great pressure caused by the immense weight of the rock layers above. This kind of regional metamorphism

5115-491: The contact area to unmetamorphosed (unchanged) country rock some distance away. The formation of important ore minerals may occur by the process of metasomatism at or near the contact zone. Contact aureoles around large plutons may be as much as several kilometers wide. The term hornfels is often used by geologists to signify those fine grained, compact, non-foliated products of contact metamorphism. The contact aureole typically shows little deformation, and so hornfels

5208-612: The crystal, producing a surface energy that makes the surface thermodynamically unstable. Recrystallization to coarser crystals reduces the surface area and so minimizes the surface energy. Although grain coarsening is a common result of metamorphism, rock that is intensely deformed may eliminate strain energy by recrystallizing as a fine-grained rock called mylonite . Certain kinds of rock, such as those rich in quartz, carbonate minerals , or olivine, are particularly prone to form mylonites, while feldspar and garnet are resistant to mylonitization. Many kinds of metamorphic rocks show

5301-402: The cultural regions of central and north Thuringia and Franconia . Dialects and traditional customs and costumes are different on either side of the Rennsteig. The Rennsteig is the subject of the song Rennsteiglied ( de ) , the unofficial hymn of Thuringia. Motorway A 4 passes north of the Thuringian Forest, while A 71 , intersecting the former south of Erfurt , crosses the range from

5394-423: The eclogite facies releases a great deal of water vapor from the rock, which drives volcanism in the overlying volcanic arc . Eclogite is also significantly denser than blueschist, which drives further subduction of the slab deep into the Earth's mantle . Metabasalt and blueschist may be preserved in blueschist metamorphic belts formed by collisions between continents. They may also be preserved by obduction onto

5487-468: The favourable climate, the Thuringian Forest is an important year-round tourist destination. Winter sports play an important role, facilities of international significance are concentrated around Oberhof. Famous sights include Wartburg Castle outside Eisenach where Martin Luther lived in exile, the selenite cave ( Marienglashöhle , a former mine) near Friedrichroda , the firearms museum in Suhl , and

5580-437: The following sequence develops with increasing temperature: The mudstone is first converted to slate, which is a very fine-grained, foliated metamorphic rock, characteristic of very low grade metamorphism. Slate in turn is converted to phyllite , which is fine-grained and found in areas of low grade metamorphism. Schist is medium to coarse-grained and found in areas of medium grade metamorphism. High-grade metamorphism transforms

5673-566: The historic town centres of Eisenach and Ilmenau . The Rennsteig trail is the most popular long-distance hiking trail in Germany. It is part of: Metamorphic rock Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism . The original rock ( protolith ) is subjected to temperatures greater than 150 to 200 °C (300 to 400 °F) and, often, elevated pressure of 100 megapascals (1,000  bar ) or more, causing profound physical or chemical changes. During this process,

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5766-449: The identical composition, Al 2 SiO 5 . Likewise, forsterite is stable over a broad range of pressure and temperature in marble , but is converted to pyroxene at elevated pressure and temperature in more silicate-rich rock containing plagioclase , with which the forsterite reacts chemically. Many complex high-temperature reactions may take place between minerals without them melting, and each mineral assemblage produced indicates

5859-437: The low-pressure facies, such as the hornfels and sanidinite facies . Most metamorphic rock is formed by regional metamorphism in the middle and lower crust, where the rock reaches the higher-pressure metamorphic facies. This rock is found at the surface only where extensive uplift and erosion has exhumed rock that was formerly much deeper in the crust. Metamorphic rock is extensively exposed in orogenic belts produced by

5952-414: The most south-eastern part of the Thuringian forest proper. It is limited by state road B 4 in the northwest, and by a line along the rivers Talwasser (with Ilmsenbach), Neubrunn, and Schleuse. The adjacent Thuringian Slate Mountains form a geographically and geologically separate natural region, although they are often popularly referred to as a continuation of the former range. Populated places wholly within

6045-529: The north. South of Georgenthal, the mountain range becomes the watershed between Elbe and Weser. Notable summits include: The B 247 from Luisenthal via Oberhof and Zella-Mehlis to Suhl , which follows the Ohra to the north, a section along the Lichtenau to the south and finally the lower reaches of the Mühlwasser , together with the slightly more than 10 km long L 1028 road that runs parallel to it to

6138-460: The northeast and the southwest clearly originate from the main one and show even and gentle slopes, not counting the steep descent into the foreland. The southwestern crests reach altitudes of about 800 m. The dividing valleys are often narrow gorges. The zone drains: The Schleuse, Gabel and Tanne feed the Schönbrunn reservoir. Notable summits include: Due to its geographical characteristics and

6231-562: The northeast to the southwest, passes under the ridge in the Rennsteig Tunnel near Oberhof, and is joined near Suhl by A 73 . Two more long-distance roads, Bundesstraßen 19 and 84, pass over the western parts of the range, while Bundesstraße 88 skirts the northern foothills between Eisenach and Geraberg. The Neudietendorf–Ritschenhausen railway crosses the Thuringian Forest in Brandleite Tunnel between Gehlberg and Oberhof,

6324-508: The northwest separates this natural sub-division of the Thuringian Forest from the rest. Apart from the south, this region is traversed by very few public roads and is only populated in the south – in the villages of Schnellbach and Struth-Helmershof in the municipality of Floh-Seligenthal , the Rotterode , Unterschönau and Oberschönau suburbs of Steinbach-Hallenberg and the town of Zella-Mehlis. The Elbe-Weser watershed , accompanied by

6417-453: The other hand, schist bedrock can pose a challenge for civil engineering because of its pronounced planes of weakness. Metamorphic rocks form one of the three great divisions of rock types. They are distinguished from igneous rocks , which form from molten magma , and sedimentary rocks , which form from sediments eroded from existing rock or precipitated chemically from bodies of water. Metamorphic rocks are formed when existing rock

6510-460: The overriding plate as part of ophiolites . Eclogites are occasionally found at sites of continental collision, where the subducted rock is rapidly brought back to the surface, before it can be converted to the granulite facies in the hot upper mantle. Many samples of eclogite are xenoliths brought to the surface by volcanic activity. Many orogenic belts contain higher-temperature, lower-pressure metamorphic belts. These may form through heating of

6603-446: The region are Frauenwald , Allzunah, Neustadt am Rennsteig , and Oehrenstock. Parts of Stützerbach also reach into this area. Roads follow the Rennsteig , the mountain crests, or the valleys of the rivers. The main ridge of the mountain range exceeds altitudes of 800 m in several places. The highest and best known summit is Kickelhahn (861 metres above sea level) southwest of Ilmenau . As seen from there, all secondary crests towards

6696-524: The relatively flat sedimentary plains of the Thüringer Becken (to the northeast) from similar rock formations in the valley of the Werra (to the southwest). It consists of a large fault block in hercynian orientation, which consists from sandstones and conglomerates of Rotliegend age in its western parts (Eisenach trough), followed by granites and gneisses of the Ruhlaer Kristallin formation of early paleozoic origin which were uplifted in

6789-475: The rock by ascending magmas of volcanic arcs, but on a regional scale. Deformation and crustal thickening in an orogenic belt may also produce these kinds of metamorphic rocks. These rocks reach the greenschist , amphibolite, or granulite facies and are the most common of metamorphic rocks produced by regional metamorphosis. The association of an outer high-pressure, low-temperature metamorphic zone with an inner zone of low-pressure, high-temperature metamorphic rocks

6882-421: The rock does not change. This is possible because all minerals are stable only within certain limits of temperature, pressure, and chemical environment. For example, at atmospheric pressure, the mineral kyanite transforms to andalusite at a temperature of about 190 °C (374 °F). Andalusite, in turn, transforms to sillimanite when the temperature reaches about 800 °C (1,470 °F). All three have

6975-458: The rock remains mostly in the solid state, but gradually recrystallizes to a new texture or mineral composition. The protolith may be an igneous , sedimentary , or existing metamorphic rock. Metamorphic rocks make up a large part of the Earth's crust and form 12% of the Earth's land surface. They are classified by their protolith, their chemical and mineral makeup, and their texture . They may be formed simply by being deeply buried beneath

7068-423: The rock to gneiss , which is coarse to very coarse-grained. Rocks that were subjected to uniform pressure from all sides, or those that lack minerals with distinctive growth habits, will not be foliated. Marble lacks platy minerals and is generally not foliated, which allows its use as a material for sculpture and architecture. Metamorphic rocks are one of the three great divisions of all rock types, and so there

7161-495: The rock typically forms mylonites. Impact metamorphism is unlike other forms of metamorphism in that it takes place during impact events by extraterrestrial bodies. It produces rare ultrahigh pressure metamorphic minerals, such as coesite and stishovite . Coesite is rarely found in eclogite brought to the surface in kimberlite pipes , but the presence of stishovite is unique to impact structures. Slate tiles are used in construction, particularly as roof shingle. Quartzite

7254-407: The rock underwent metamorphism. These minerals are known as index minerals . Examples include sillimanite , kyanite , staurolite , andalusite , and some garnet . Other minerals, such as olivines , pyroxenes , hornblende , micas , feldspars , and quartz , may be found in metamorphic rocks but are not necessarily the result of the process of metamorphism. These minerals can also form during

7347-486: The rock). Metasedimentary rocks are divided into carbonate-rich rock (metacarbonates or calcsilicate-rocks) or carbonate-poor rocks, and the latter are further classified by the relative abundance of mica in their composition. This ranges from low-mica psammite through semipelite to high-mica pelite . Psammites composed mostly of quartz are classified as quartzite. Metaigneous rocks are classified similarly to igneous rocks, by silica content, from meta-ultramafic-rock (which

7440-572: The same time, are the bordering Zechstein deposits which contain Bryozoa reefs. These stretch especially wide on the northwestern edge of the Thuringian forest, where the landscape park of Altenstein Palace is located on one of the largest Zechstein reefs in Germany. The Eisenach trough is part of the much larger Werra basin, which in turn is part of the Saar-Unstrut depression of early Permian origin. It

7533-406: The sedimentary rock limestone and chalk change into larger crystals in the metamorphic rock marble . In metamorphosed sandstone, recrystallization of the original quartz sand grains results in very compact quartzite, also known as metaquartzite, in which the often larger quartz crystals are interlocked. Both high temperatures and pressures contribute to recrystallization. High temperatures allow

7626-718: The south, and by the Variscan rocks of the Thuringian Highland towards the east. The geological borders differ from the geographical ones insofar, as the Rotliegend rock of the Thuringian forest finds its continuation in the Masserberg and Crock block in Hildburghausen district , southeast of the main range, and the rock types of the Thuringian Highland are also found in the Schleuse horst between Schönbrunn reservoir and Schönau, and in

7719-404: The temperatures and pressures at the time of metamorphism. These reactions are possible because of rapid diffusion of atoms at elevated temperature. Pore fluid between mineral grains can be an important medium through which atoms are exchanged. The change in the particle size of the rock during the process of metamorphism is called recrystallization . For instance, the small calcite crystals in

7812-448: The towns Eisenach , Gotha and Arnstadt . The towns of Ilmenau and Suhl sit in slight dips on the range itself to the north and south respectively. The Thuringian Forest forms a continuous chain of ancient rounded mountains with steep slopes to both sides and poses ample difficulties in transit routing save through a few navigable passes. It is about 70 km (43 mi) long and 20 km (12 mi) wide. The highest elevation

7905-454: The typical reddish molasse sediments (conglomerates, sandstones, siltstones, and claystones) of the Rotliegend. The Little Thuringian Forest (German: Kleiner Thüringer Wald ) is a narrow horst south of Suhl and northwest of Schleusingen , northwest of Schleuse river, embedded in the Triassic foothills of Southern Thuringia. It is oriented roughly parallel to the Thuringian Forest and, while

7998-461: The upper Devonian were subjected to intense metamorphosis during the Variscan uplift and are now mostly present in the form of gneiss or schist . The Oberhof trough is by far the largest of the main geologic parts of the Thuringian Forest. It consists of the uplifted part of the so-called Thuringian Forest Basin whose contents can be further subdivided into several formations. Their relative ages have not been fully resolved yet, partly because

8091-451: The use of granulite as a classification for rock metamorphosed to the granulite facies. Instead, such rock will often be classified as a granofels. However, this approach is not universally accepted. Metamorphic rocks make up a large part of the Earth's crust and form 12% of the Earth's land surface. The lower continental crust is mostly metamafic-rock and pelite which have reached the granulite facies . The middle continental crust

8184-402: The valleys of the rivers Schilfwasser and Schmalkalde and passes through Kleinschmalkalden and state road 1028 between Georgenthal and Floh-Seligenthal which follows the valleys of the rivers Apfelstädt and Flohbach divide the area into segments. In this area the mountain ridge becomes more pronounced. The summit of Großer Inselsberg of volcanic origin causes a marked shift of the ridge towards

8277-561: The zonal schemes, based on index minerals, that were pioneered by the British geologist, George Barrow . The metamorphic facies is not usually considered when classifying metamorphic rock based on protolith, mineral mode, or texture. However, a few metamorphic facies produce rock of such distinctive character that the facies name is used for the rock when more precise classification is not possible. The chief examples are amphibolite and eclogite . The British Geological Survey strongly discourages

8370-482: Was given up as unprofitable due to difficult drainage. Large baryte deposits prospected in the 1950s have remained untouched. The Waltershausen foothills (German: Waltershäuser Vorberge ) are a wooded chain of Buntsandstein hills immediately north of and parallel to the Thuringian Forest between Eisenach, Waltershausen, Friedrichroda, and Georgenthal. An outcrop of Muschelkalk rock can be found in their northern part, south of Waltershausen. They are generally regarded

8463-419: Was important in metamorphism. This hypothesis was tested by his friend, James Hall , who sealed chalk into a makeshift pressure vessel constructed from a cannon barrel and heated it in an iron foundry furnace. Hall found that this produced a material strongly resembling marble , rather than the usual quicklime produced by heating of chalk in the open air. French geologists subsequently added metasomatism ,

8556-639: Was part of the Saxonian tectonic processes and is understood as a long range effect of the Alpine orogeny . It began in the upper Cretaceous era and ended in the late Tertiary after about 40 million years. Thuringian forest is surrounded on three sides by triassic rocks: the Thuringian Basin in the northeast, the Hesse Highlands in the west, and the northeastern parts of the South German Scarplands in

8649-431: Was uplifted as one of the fault blocks in the Saxonian tectonic era and is filled with Variscan molasses , named Eisenach formation after the location. It consists mostly of monotonous sequences of reddish conglomerates representing a proximal alluvial fan which originated in debris flows from the Ruhla anticline. Dated in the upper Rotliegend, the Eisenach formation consists of some of the youngest geological units in

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