Ox head proterobas
Ochsenkopf-Proterobas , also called Ochsenkopf , Grünstein , Fichtelgebirgsporphyr or Green-Porphyry , is a lamprophyr , a basic gangue rock . The dark green Ochsenkopf Proterobas was broken on the Ochsenkopf mountain of the same name in the Fichtel Mountains until 2009 .
Geology, rock description and mineral inventory
The Proterobas was created in the Permian . It is a lamprophyre , a fine-grained dike rock that has undergone a weak metamorphosis after its formation.
White plagioclases are in a green mass of pyroxene and amphibole . The green color is caused by chlorite and serpentine . Partly pyrite occurs. The Proterobas is a medium-grain, dark green and white speckled rock. Proterobas contains plagioclase with 49 percent, muscovite , chlorite and serpentine 15 percent, pyroxene 16 percent, ores 8 percent, hornblende 4 percent, biotite and quartz each 3 percent. With a total of 2 percent, accessories are epidote / zoisite , rutile and apatite .
Naming
The ox-head proterobas was given different names. In the past, diabase were called green stones . The name Fichtelgebirgsporphyr goes back to the porphyry-like arrangement of the minerals in the rock. From a geological point of view, it is not a porphyry, but a basalt or a metabasalt, a diabase.
Occurrence
The Proterobas runs through a rock between Bischofsgrün and Fichtelberg as a passage , which stretches in a length of about 8 km and a width of 5 to 30 meters in a southeast-northwest direction through the mountain massif over the mountain Ochsenkopf .
use
Proterobas was already being mined there in the early Middle Ages and made into glass buttons and hollow glasses. During archaeological excavations in 2004 it was found that the stone material was melted in button glass works from the middle of the 17th century and processed into black glass and subsequently into glass buttons and glass beads. Scientific research by the University of Bayreuth is still ongoing. In the late 17th century, the so-called ox-head glasses were made in Bischofsgrün .
As a natural stone , it was mainly used for gravestones and memorials, fountains and stair and floor coverings as well as paving until the 1950s. Like granite, Proterobas is weatherproof and can be polished. This natural stone was used on the stairs of the courthouse and for fountains in Würzburg and in the vestibule of the Reichstag building in Berlin.
In the Third Reich , Proterobas was a stone that was preferred by Arno Breker , Fritz Klimsch , Josef Thorak and Artur Sansoni for stone carving work, as it has a granite-like appearance, but is easier to work than granite due to its lower hardness.
literature
- Wolf-Dieter Grimm: picture atlas of important monument rocks of the Federal Republic of Germany. Published by the Bavarian State Office for Monument Preservation, Lipp-Verlag, Munich 1990, ISBN 3-87490-535-7 .
- Dietmar Herrmann: Proterobas glassworks on the Ochsenkopf . In: Der Siebenstern 2007, ISSN 0949-4685 , pp. 5–6.
- Friedrich Müller : Bavaria's rich corner. Geological history, rocks, minerals, fossils from the Fichtelgebirge, Franconian Forest, Münchberger Masse and northern Upper Palatinate Forest . 2nd expanded edition. Oberfränkische Verlags-Anstalt, Hof 1984, ISBN 3-921615-24-0 .