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Silvretta Crystalline

by Theresa König last modified 2008-02-19 14:48

Silvretta Crystalline

The rock of the Silvretta Crystalline is crossed in the first and last part of the trail. The rock is explained on two geological plates. These rocks build up the underground of the church in Bartholomaeberg and also of the slopes down to the valley floor. The mountain chains to the south-east and east like Hochjoch, the Verwall and the Silvretta group and the green slopes of the Rätikon mountains to the south are part of the Silvretta Crystalline.
These rocks are the oldest rocks in Vorarlberg, parts of which are more than 1.5 billion years old. The rocks were metamorphosed during at least three mountain building phases which are called orogenies. The last decisive metamorphic overprint took place about 325 million years ago.  During the following 200 million years the sedimentary rocks of the “Northern Calcareous Alps” were sedimented on the basement of the Silvretta Crystalline.
During alpine times the Silvretta Crystalline and the overlying Northern Calcareous Alps were thrust over 2,000 km to the north-west as a result of the tectonic movements of the African plate. Despite several metamorphic overprints the source rock of the Silvretta Crystalline can be identified: Sandstones, marls and clays were transformed into phyllites, mica schists and paragneisses; former volcanic ash and lava was transformed into green amphibolites. Hornblende gneisses, augen- and flasergneisses resulted from earlier granites. As the gneisses and mica schists of the Silvretta Crystalline are rich in minerals, they provide ideal conditions for plants that can be traced in altitudes up to more than 3,200 metres above sea level.
Plates 1 and 24 of the Bartholomaeberg Geology Trail display typical rocks of the Silvretta Crystalline. Table 1 shows mineral-rich paragneisses and mica schists.  On the right upper slope of the road going up to the “Linde”, you can see  Biotite-staurolite-micaschists with light-grey quartz, milky feldspar and large black mica (also called ”fools gold” and white mica which is known as “fools silver”  as well as dark-brown or black needles of staurolithe .


P01-6 Silvretta Crystalline.mp3

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