Revisiting a geo-tourism attractions in Freisen ( Saarland)
Author: Michael Hahl MA, geographer
high above the Freisen roofs of the village in Saarland Landkreis St. Wendel covers the back of Heller's summit with its breathtaking view from 596 meters above sea level. Figure 1 (Record: Hahl) shows him from the hamlet of Upper Church viewed from.
In the abandoned quarry at the Heller mountain was mined for decades andesite. It is an igneous volcanic rock, which was formed in a phase of the Permian volcanism, before over 270 million years ago. Today can be the Hellerberg still detect several former lava flows, and in marginal zones amygdaloid made the local mineral collectors agate fascinating finds, in the minerals in the district and museums in Freisen Obernkirchen can be seen (Figure 2: Example of an agate discovered in the museum Upper churches, recording: Hahl) .
"beheaded" Magmenintrusion
On some places, shows platy andesite-Hellberger spin-offs, which are prominent in the predominantly compact magma rock. For this form of wealth is ultimately also an impressive semi-circular stone structure, which is about 15 feet tall emerges from a quarry wall (Figure 3, mounting: Hahl) .
The emergence of these "Basalt Rose" or "Basalt rosette", as she has been referred to colloquially, raises a puzzle: Some see it as quite the stone has become evidence of a .. advancing lava flow (see Laarman, Ursel, no date, The Gift of the Permian volcanoes In: The agate gem is created from the Idar-Oberstein extraLapis No. 19, p. 29; MINERALS ASSOCIATION Freise, 2008.. Highlights from the center of the agates. P.4) . Other experts maintain that form, however for the digestion of an upwardly dome-like intrusion, that is the remnant of a magmatic melt into it expressed itself in the already solidified volcanic rock (see SCHNEIDER, Horst, 1991, collection of geological guide. Saarland. S. 188) .
The estimation of the Geological leader I concur. A penetrating the Andesitkomplex and ultimately the erosion of "decapitated" Magmenintrusion is in the field and in the context of the volcanic lava-Hellerberg well comprehensible interpretation of the digestion (see illustration, graphic design: HAHL, Michael, 2010, the first time published) .
After that was chemically also freigenagt as andesite to be addressed intrusion, that is the underground tunnel of rock, from the millions of lasting erosive effect, formed as a result of pressure relief and weathering of surface-parallel cracks and semi-circular detachment surfaces. Unknown why there is the angle at which the intrusion may have entered through the Andesitkörper; unique flow structures were not found until now.
through a window into the Earth can marvel at the remarkable Hellerberg today andesite intrusion in cross section. - Probably today's disk-like shape was even once crowned pronounced hemispherical respectively, because of the lower part of the strange rock structure at the quarry wall is not disrupted. The characteristic skin weathering of igneous rocks is the spherical shaping not so rare. Figure 4 (source: wikipedia) shows for comparison the so-called "Stone Rose" in the Thuringian town hall castle Ebersdorf, certainly also the work of weathering, erosion are coupled to a pressure relief. "Basalt Rose, Andesitrose" or "Freisener rock disc"?
"Basalt Rose" - that sounds good, and yet the name does not geoscientifically treatment and thus not in the sense of a high-quality geo-tourism development. That it is not basalt, but the quartz-rich andesite is generally known. Basalt assignment should come from everyday language of the popular Quarry terminology and was probably continued since in the vernacular, as in many other stone quarries "basalt-like" rocks as well - such as the hunchback in the southern Odenwald, whose "basalt rocks" to be precise as phonolite and syenite are addressing ( see AK SCHMITT, MARK MA, NESBOR HD, Markle G., 2007, The onset and origin of differentiated Rhine Graben volcanism based on U-Pb ages and oxygen isotopic composition of zircon, Eur J. Mineral., 19, pp 849-857.) .
However, the terms "rosette" and it inspired, "Rose" are geologically for a different kind, namely a "hedgehog-like, radial pillar formation in igneous rocks. Image Example 5 shows the basalt subjects on Hirtstein in Saxony Erzgebirge (Record: Steve Moeckel, source: wikipedia). 
What name the stately "Basalt Rose" or "Basalt rosette" of Hellerberg (image section 6; Recording: Hahl) future they will take now is, of course, decide to be in Freisen itself. Perhaps the engaged citizenry is a fitting new name for their " Freisener rock ball " a? " andesite intrusion ?" Or " Freisener rock disc "? " Steinerner semicircle on Hellerberg " perhaps? Or rather quite traditional " Andesitrose ? On the day of the Geotops on September 19, 2010 organizes community Freisen, together with the mineral association Freisen a guided hike to the spectacular Geotop on Hellerberg details about your visit.:
http://www.netzwerk-freisen.de/index.php?option=com_content&task=view&id=100&Itemid=82
Look einnal also refer to the side of Freisener mineral association:
http://www.mineralienverein-freisen.de/de/news/news_120910.html
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