Scarf stone

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The Schalstein , also Blatterstein , is a slightly metamorphic volcanic - volcanoclastic rock with a basaltic composition, which in the Devonian of the Central European slate mountain eruptions ( Rhenish Slate Mountains , Harz , Thuringian-Franconian-Vogtland Slate Mountains ) sometimes forms thick strata.

Origin of name

The term "greenstone" was of Nassau shaped miners since the rock during mining of iron ore because of its foliation split often cupped. The term was introduced into geological literature by Johann Philipp Becher in his work "Mineralogical Description of the Orange-Nassau Lands" in 1789 and has since served as an umbrella term for paleozoic volcanoclastic rocks. Today the term is only used as a stratigraphic collective term in geology , as the rocks summarized under this term come from the Middle and Upper Devonian and are therefore of different ages.

Rock and formation

The scarf stone has a very different appearance due to the diversity of the rocks grouped under this term. Usually it has a gray, greenish, yellowish or reddish color or is spotty. Often the rock is shale, often massive and structureless. Calcite is not infrequently mixed in in nests and rubble . The original basic mass of volcanic rock glass ( sideromelan ) has mostly changed today, and its main components can only be recognized under the microscope on the basis of characteristic shapes as fragments of volcanic glass . The scarf stone often contains debris from adjacent rocks, both of volcanic and sedimentary origin.

The rock was formed as a submarine deposit of volcanic ash in connection with the formation of extensive submarine volcanic structures that built up in the Devonian on the passive continental margin of the Rhenohercynic . Together with the scarf stone, lava flows were involved in the formation of the submarine volcanoes. Some of the volcanic structures towered above sea level, creating atolls . Associated with volcanism was the discharge of mineral-rich waters on the sea floor, so that extensive deposits of iron ore ( Roteisenstein ) could form. For this reason, the scarf stone often occurs today together with limestone and red iron stone . The phosphorite, which also often occurs in connection with the scarf stone, comes from the weathering of the limestone.

Occurrence

The most extensive deposits of scarf stones are known from the Lahn and Dill basins of the slate mountains on the right bank of the Rhine, south, south-east and east of the Westerwald . They can also be found as a continuation of the slate mountain occurrences in the Harz, for example in the area around Clausthal-Zellerfeld and above all near Elbingerode .

The term scarf stone was also applied to volcanoclastic rocks outside of the Rhenish Slate Mountains and the Harz Mountains, for example to Silurian volcanic rocks near Prague .

The rock - especially in its massive variant - was often used as building material in its occurrence areas, for example for houses, churches and bridges. However, since it is very sensitive to weathering, the preservation and restoration of structures built from it is problematic.

photos

  • Cut of a Devonian shell stone

Individual evidence

  1. ↑ Schalstein. Meyers Konversations-Lexikon, 4th edition from 1888 to 1890.
  2. ↑ August Reuss: Mineralogical Notes from Bohemia. About Silurian scarf stones and the iron ore deposit of Auval near Prague. Meeting reports of the Imperial Academy of Sciences, Vol. 25, pp. 341–363.
  3. ^ JM Deinhard: Description of the Elbbach bridge Niederhadamar - St. Wendelin bridge. ( Memento of the original from September 27, 2007 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. Stone bridges in Germany, 1988, ISBN 3-7640-0240-9 . @1@ 2Template: Webachiv / IABot / www.baufachinformation.de
  4. ↑ The preservation of the heath portal at Wetzlar Cathedral. Novel approaches to preserving a problem rock. Final report on the DBU project AZ 19537: Model-like conservation and restoration of environmentally damaged shell stone on the Romanesque heather portal of the Wetzlar cathedral.

literature

  • Joe-Dietrich Thews: Explanations of the geological overview map of Hesse 1: 300,000 . In: Geological treatises Hessen . tape 96 . Hessian State Office for Soil Research, Wiesbaden 1996, ISBN 3-89531-800-0 , p. 122 f .
  • Heinz-Dieter Nesbor, Werner Buggisch, Heiner Flick, Manfred Horn, Hans-Joachim Lippert: Volcanism in the Devonian of the Rhenohercynic. Facial and palaeogeographical development of volcanic marine basins using the example of the Lahn-Dill area . In: Geological treatises Hessen . tape 98 . Hessian State Office for Soil Research, 1993, ISSN  0341-4043 .
  • Kurt Mohr: Geology and mineral deposits of the Harz . 2nd Edition. E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart 1993, ISBN 3-510-65154-5 , p. 52-65 .

Web links