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The former Basalt quarry at the Arensberg, is situated approx. 1km northwest of Zilsdorf. The Arensberg or Arnulphusberg, is the only major volcanic dome in the area around Zilsdorf-Hillesheim. The volcanic activity dates from the Tertiary period. The two outbreak periods date from around 24-32 million years ago.
During the first phase of the outbreak of the Arensberg-volcano, the magma penetrated the ascending sandstone layers from the Lower Devonian time, the layers of limestone and sandstone Mid Devonian time and limestone strata from the Triassic era.
Based on the sandstone and limestone-rock inclusions in the basalt lava and tuffs of the Arensbergs, it can be confirmed that, at the time of the first outbreak more layers of rock from the Triassic time were covering the area.
In the entrained blocks of limestone, Calcic minerals were formed, due to the contact with the hot lava streams. On the contact zones between the carbonate host rocks and the basalt, little cavities were formed, which are filled with mineralizations.
There were three distinct types of cavities: 1st - incompletely filled cavities, 2nd - completely filled cavities and 3rd - inclusions in Devonian limestones.
In cavities from the first type, it was easy to recognize some first generation Calcite and often there are clearly recognizable Phillipsite crystals visible.
In cavities from the second type, you could also find Phillipsite, covered with radiated Thomsonite. Within the Thomsonite covered cavities you could find minerals like Aragonite, Calcite, Montmorillonite, Tacharanite, Tobermorite and Vaterite.
And in the inclusions in the limestone you could find minerals like Artinite, Brucite, Calcite, Dolomite, Hydromagnesite, Hydrotalcite, Montmorillonite and more.
This locality is lying within a nature reserve, so searching for minerals is not allowed.
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If you're searching for mineralogical articles on this locality (Der Aufschluss - Jahrgang 29 - 1978 Heft 7/8: Die Minerale des Arensberges), please contact us...
Also see: Geo-Pfad Hillesheim, Geoberg.de, Jose Dehove, MinMax, Mineralienatlas,
Mindat.org on this location.
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