Trachyte
Trachyte, derived from the Greek word τραχύς ( trachys ) with the meaning rough, is a volcanic rock. He was described and named for the first time by the French mineralogist Alexandre Brongniart in 1813.
Etymology and history
As Alexandre Brongniart type locality were used for its description volcanic rocks from Auvergne. During the cooling of the trachytes escaping gas phase forms tiny, irregular cavities, which then give the rock in fresh fracture a rather rough, jagged appearance - hence also Brongniarts neologism explained.
Other names for trachyte, such as Orthophyr, Ortho porphyry and orthoclase porphyry, are outdated and should no longer be used.
Chemical composition
Chemically, trachyte identical to the plutonic rock syenite and ensure its on the surface solidified equivalent dar. In QAPF classification diagram after Streckeisen is trachyte in box 7 However, if its modal composition is not recognizable, it is chemically defined by the T TAS field. Its SiO2 content varies from 57.6 to 69 weight percent and is lower than that of rhyolite. The alkali oxides Na2O and K2O are more than 7 percent by weight and are higher than in dacite.
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 over plagioclase than 90 percent by volume, one (6 field in the Streckeisen diagram ) speaks of a Alkalifeldspattrachyt. Furthermore, up to 20% quartz ( or quartz Quarztrachyt Alkalifeldspattrachyt ) or up to 10 % of the minerals Foidgruppe ( foid - leading trachyte or foid - leading Alkalifeldspattrachyt ) can be added. Subordinate occurring mafic components are clinopyroxene, hornblende, biotite, fayalite and others. Because of mineral deposits results in a bright color of the rock. Frequently porphyritic texture with phenocrysts of these minerals in a glassy or fine-grained feldspathic matrix can be observed. Some forms of this type are referred to as Rhombenporphyr and are known as part of Scandinavian boulders.
Trachyte can also be in the form of obsidian or as pyroclastic rocks ( eg pumice ) occur.
Occurrence
Trachyte is a common rock in many volcanic regions worldwide. In Germany in particular, the occurrence in the Westerwald and the Seven Mountains are mentioned. Also on hessian Vogelsberg trachyte is not rare. Near the Hoherodskopf, a 14 million year old volcanic chimney of basalt, trachyte an existing intrusion has been identified in a bore in the 200 m depth.
Already in Roman times the trachyte was mined from the Drachenfels, the average age of the Drachenfels trachyte was the most important component for statically loaded parts from the Seven Mountains down the Rhine. In the early 13th century began with the dismantling of the Trachytes in Wölferlingen for Marienstatt Monastery. Later workings came in seltzer (Westerwald ) (since about 1770) and in Weidenhahn (1848 ) added. Further reduction places are in Reimerath near Mayen in the Eifel. About the rivers of stone was shipped to the Rhineland and to the Netherlands. The Romanesque churches of Cologne were set up so that after the Second World War.
In Europe, there is relatively little degradation places: in Italy is - so far outside the protected area of the Natural Park - in the Euganean Hills near Padua and in Bosa in Sardinia, in Norway at Modum near Oslo and the Czech Republic at Heřmanov ( Hermann village) at Karlovy Vary degraded trachyte.
Trachyte is used for church furnishings, walls, floors and in the garden area. It is frost resistant and restricted polished.
Types of natural stone
- Trachyte Weidenhahn ( Weidenhahn in Rhineland -Palatinate )
- Trachyte Seltzer ( Seltzer (Westerwald ) )
- Teplá ( Hermanovsky trachyte ) ( Czech Republic)
- Algersdorf ( Valkeřický trachyte ) ( Czech Republic)
- Trachite Euganean Hills (Padova, Italy)