Trachyte
Trachyte , derived from the Greek word τραχύς trachys meaning "rough", is a volcanic rock . It was first described and named by the French mineralogist Alexandre Brongniart in 1813.
Etymology and history
Alexandre Brongniart used volcanic rocks from the Auvergne as the type locality for his description . When trachytes cool down, the escaping gas phase forms tiny, irregular cavities, which then give the rock in the fresh fracture a rather rough, jagged appearance - this explains Brongniart's creation.
Other names for trachyte, such as B. Orthophyr , Orthoporphyr and Orthoklasporphyr are obsolete and should no longer be used.
Chemical composition
Chemically, trachyte is identical to the deep rock syenite and represents its solidified equivalent on the surface of the earth. Trachyte is in field 7 of the QAPF classification diagram according to Fahrtisen . However, is its modal composition is not visible, it will chemically by the TAS field T defined. Its SiO 2 content varies between 57.6 and 69 percent by weight and is less than that of rhyolite . The alkali oxides Na 2 O and K 2 O amount to more than 7 percent by weight and are thus higher than in Dacit .
Mineralogical structure
Trachyte consists mainly of alkali feldspar ( sanidine and orthoclase ) and sodium-rich plagioclase , with the former predominating. If the proportion of alkali feldspar compared to plagioclase is over 90 percent by volume, one speaks of an alkali feldspar trachyte (field 6 in the iron line diagram). Furthermore, up to 20% quartz ( quartz trachyte or quartz alkali feldspar trachyte ) or up to 10% minerals of the foid group ( foid-carrying trachyte or foid-carrying alkali feldspar trachyte ) can be added. Subordinate mafic components are clinopyroxene , hornblende , biotite , fayalite and others. Due to the mineral content , the rock color is light. A porphyry structure with interlocking of the minerals mentioned in a glassy or fine-grain feldspar matrix can often be observed. Some forms of this type are called rhombic porphyry and are known as part of Scandinavian bed load .
Trachyte can also occur in the form of obsidian or as pyroclastic rock (e.g. pumice stone ).
Occurrence
Trachyte is a common rock in numerous volcanic areas worldwide. In Germany, the occurrences in the Westerwald and in the Siebengebirge should be mentioned in particular . Trachyte is also not uncommon on the Hessian Vogelsberg . In the vicinity of the Hoherodskopf , a 14 million year old basalt volcanic vent , an intrusion consisting of trachyte was identified during a drilling at a depth of over 200 meters .
The trachyte from the Drachenfels was already dismantled in Roman times , in the Middle Ages the Drachenfels trachyte was the most important building block for statically stressed components from the Siebengebirge down the Rhine. In the early 13th century, the trachyte was mined in Wölferlingen for the Marienstatt monastery . Mining operations were later added in Selters (Westerwald) (from around 1770) and in Weidenhahn (1848). Other mining sites are in Reimerath near Mayen in the Eifel . The stone was shipped across the rivers to the Rhineland and the Netherlands. The Romanesque churches in Cologne were, as the Drachenfelser Bruch had exhausted itself in the 18th century, usually rebuilt with Selterser Trachyte after the Second World War. This affected components with a load-bearing function, the walls were built up with tuff, mostly from Weiberner tuff , as in the destroyed medieval churches .
Trachyte was also extracted in southern Hesse, for example on the Hohe Berg in Heusenstamm and probably also in the neighboring Gravenbruch , whose name comes from the "gray break", i.e. trachyte.
There are relatively few mining sites in Europe: in Italy - so far outside the protected zone of the nature park - in the Euganean Hills near Padua and in Bosa on Sardinia , in Norway near Modum near Oslo and in the Czech Republic near Heřmanov (Hermannsdorf) near Karlovy Vary and in France in the Auvergne Trachyt mined. Other deposits are located near Cripple Creek in the US state of Colorado and on the island of Tenerife .
Trachyte is used for church furnishings , facades, floors and in the garden area. It is frost-resistant and can be polished to a limited extent.
Natural stone types
- Trachyte Weidenhahn ( Weidenhahn in Rhineland-Palatinate )
- Selters-Trachyte ( Selters (Westerwald) )
- Teplá (Heřmanovský trachyt) (Czech Republic)
- Algersdorf (Valkeřický trachyt) (Czech Republic)
- Trachite dei Colli Euganei ( Padua , Italy)
See also
literature
- Richard V. Dietrich, Brian J. Skinner: The rocks and their minerals. An introduction and identification book. Ott, Thun 1984, ISBN 3-7225-6287-2 .
- Walter Maresch, Olaf Medenbach: Rocks . With the collaboration of Hans Dieter Trochim. Edited by Gunter Steinbach . New, edited special edition. Mosaik-Verlag, Munich 1987, ISBN 3-576-10699-5 ( Steinbach's natural guide ).
Web links
Individual evidence
- ↑ The research borehole at Rehberg ( Memento of the original from March 1, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Bonewitz, Ra., Burgess, Linda., Astor, Ellen: Stones & Minerals: [Rocks, minerals, precious stones, fossils] . Dorling Kindersley, Munich 2009, ISBN 978-3-8310-1469-9 .
