Rogenstein

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Roe stone from the Lower Buntsandstein, Heeseberg quarry, Helmstedt district
Rogenstein, pending in the Heeseberg quarry
Sangerhausen town hall

Roe stone is a traditional petrological name for a special type of oolithic limestone . The main rock components of this rock are relatively large, originally calcitic ooids , whose concentric structure is very well preserved. The similarity with fish eggs led to the name Rogenstein , it was applied to the oolites in the Lower Buntsandstein of northern Germany and oolites in the Middle Jura of southern Germany. For the latter, the name was and is even used in the sense of a lithostratigraphic unit ( main roe stone formation).

education

The components of the roe stone, the ooids, were formed in warm, strongly turbulent shallow seas. It is important in this context that the ooids were originally calcitic and are relatively large (up to 12 mm in diameter). The concentric shell structure of the ooids is therefore usually very well preserved. In contrast, today's ooids are aragonitic and significantly smaller. The concentric structure of the ooids is only difficult to recognize in subrecent oolites or solidified ooid sands, since the isochemical recrystallization and conversion of the aragonite into calcite begins quite early. The formation of aragonitic or calcitic ooids depends primarily on the relative Mg content of the seawater. If this is low, calcitic ooids are formed; if it is high, aragonitic ooids are excreted. Relatively high Mg contents occur above all in times with ice ages ("ice house"), low Mg contents in times without ice caps ("green house"). However, this is only a general tendency that can be modified by local factors.

Occurrence

Roe stones are widespread in northern Germany in the southern, northern and eastern Harz foreland in the Lower Buntsandstein ( Triassic ). The deposits stretch from Nordhausen , Sangerhausen , Mansfeld to Bernburg , from Thale via Heeseberg , Dorm to the Salzgitter mountain range. The mightiest benches are found at Jerxheim with a thickness of 6 meters and in the Bernburg area with 4 to 6 meters. There were larger quarries between Mansfeld, Bernburg and Alsleben an der Saale , and there used to be numerous quarries with local names such as the Nussberg in Braunschweig ( Braunschweiger Rogenstein ). The benches are designed differently. There are locations with 3 to 5 banks, on the ridge near Salzgitter, in the Harly Forest , in the Asse and its eastern branch, the Heeseberg , there are 10 to 12 banks. But there are also thinner layers that are separated by clay-sandy deposits. At Bockenem , around Halberstadt and Quedlinburg , the number of benches is falling sharply. Today (2008) there is no longer any quarry for the extraction of natural stone .

Other deposits are in southwest Germany, in Baden-Württemberg near Riegel am Kaiserstuhl , and further north of Basel . These roe stones come from the Dogger . In the case of these deposits, the name Rogenstein was even included as part of a rock unit of lithostratigraphy , the main Rogenstein Formation.

Use and structures

Orangery built from Rogenstein in Wernigerode

The roe stones were previously used as stone , paving stones, curbs, solid steps and cattle troughs. It is a hard and tough stone that is very difficult to work with by hand or to process into profiles. It has been used as a building block in northern Germany and as a brick since the 11th century.

Here are some selected places and structures:

literature

  • Wilhelm Dienemann and Otto Burre: The usable rocks in Germany and their deposits with the exception of coal, ores and salts , Enke-Verlag, Stuttgart 1929, p. 363f
  • Otto Sickenberg: stones and earth. The deposits and their management. Geology and Deposits of Lower Saxony , 5th vol. Dorn-Verlag, Bremen, Horn 1951, p. 279ff.
  • Erik Flügel : Microfacies of Carbonate Rocks. Springer-Verlag, Berlin, Heidelberg, New York 2004, ISBN 3-540-22016-X

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