Fritted rock
A rock that has emerged from pyrometamorphosis or combustion metamorphosis and contains up to a maximum of 20% glass is called fritted rock .
Historical development of the name
The term “fritting” for the corresponding process of contact metamorphosis was used in the English-language geological literature as early as the early 19th century. In Germany, the geologist August von Klipstein used the term "fritted" to describe the rocks from the Wildenstein near Büdingen in the Wetteraukreis in the southwestern foreland of the Vogelsberg , which were created by the intrusive contact of red sandstone with basalt. In this work, the term Buchit was coined, which is used today for corresponding rocks with a higher glass content.
A clear distinction between the terms “buchit” and “fritted rock” was only achieved through the definition of the International Union of Geological Sciences . In the past, these terms were also used synonymously, since a quantitative determination of the glass phase was not important at that time.
Education and occurrence
Like the buchites, the fritted rocks are also found in the metamorphic sanidinite facies ; This means that they were formed at high temperatures (above 800 ° C), but at normal pressure or only slightly increased pressures, for example through underground coal fires or through direct contact with molten magma at a comparatively shallow depth.
A well-known occurrence in Germany is the “Bühlchen” near Epterode in Northern Hesse, where the metamorphosis was triggered by burning brown coal seams.
Outside Central Europe known deposits are located approximately in the Plataubasalten the East or West Fjords of Iceland . Here eruptions of volcanic flood basalts took place at intervals, which regularly buried large areas of the former land surface and subjected the soils that had formed between the eruptions on the surface of the older plateau to a contact metamorphosis. A particularly striking example can be found at Hengifoss in the east fjords.
Appearance in the field and response
Like Buchite, fritted rocks can have both a slag-like and dense appearance. Often noticeable are the changes in the color of the rock due to the heat, which can range from white to yellow and red to gray-black. The reliable differentiation of Buchites requires a determination of the glass content, which can usually not be achieved in the field. Likewise, products of human activity such as slag from smelting processes or fragments from brickworks products can be macroscopically difficult to distinguish.
literature
- Roland Vinx: Rock determination in the field. 3rd edition, Spektrum, Heidelberg 2011, ISBN 978-3-8274-2748-9 .
- Rodney Grapes: Pyrometamorphism. 2nd edition, Springer, Heidelberg 2011, ISBN 978-3-642-15587-1 .
Individual evidence
- ↑ a b D. Fettes, J. Desmons (Ed.): Metamorphic Rocks. University Press, Cambridge, 2011, p. 153
- ↑ SI Tomkeieff: Dictionary of Petrology. Wiley, Chichester, 1983, p. 209
- ↑ A. v. Klipstein: About vulcanized sandstones in the Vogelsgebirge . In: Hertha magazine for geography, ethnology and national studies . tape 10 . Stuttgart 1827, p. 354-368 .
- ↑ Wolfram Echle: The porcelain jasper from Epterode . In: Association of Friends of Mineralogy and Geology (Hrsg.): Der Aufschluss . Special volume 28. Heidelberg 1978, p. 205-209 .