Löbejun porphyry
The Löbejun porphyry , also Löbejun rhyolite , is a Felsic volcanite of reddish color (exact petrographic name: Alkalifeldspar - Rhyolite ) and an economically important natural stone .
Occurrence
The rock occurrence of the Löbejün porphyry bites out in the vicinity of Löbejün , about 10 km north of Halle (Saale) in Saxony-Anhalt on about 5 km². Below the predominantly Cenozoic outer layers, the Löbejün porphyry body extends to shortly before Halle; its north-south extension is about 10 km, its east-west extension 5 km. It reaches a thickness of more than 800 meters, the total volume is more than 60 km³.
Regional geologically, the Löbejün porphyry is part of the Hallesches volcanic complex in the north-east of the Saale depression , which in an area of 500 km² in total , is only one of many similarly old rhyolite complexes in Central Europe (e.g. south-eastern Thuringian Forest , Donnersberg ).
The Löbejun porphyry was created sub-volcanically in the form of a laccolith on the Stefanium - Rotliegend border approx. 298 million years ago, where it was placed in layers of the Siebigerode Formation (Stefanium C).
properties
The Löbejun porphyry is a volcanic rock. In addition to its origin, it is named after its typical porphyry structure : in a finely crystalline, reddish base mass (proportion approx. 66%), larger mineral grains ( insects ) of pink and light gray, up to 30 mm large feldspars (plagioclase, orthoclase ) are distributed in a directionless, granular manner ) and gray crystals . Since the Einsprenglinge are relatively large compared to other porphyry rhyolites, the Löbejun porphyry is also referred to as a "large porphyry". The jets formed in the magma chamber before the final ascent of the melt and the formation of the laccolith. The reddish color of the rock results from accessory admixtures of hematite and magnetite in the fine-grained matrix.
The chemical composition of Löbejun porphyry, like that of all rhyolites, is very similar to that of granites. The rock consists of the following main mixture parts: approx. 72% SiO 2 , approx. 13% Al 2 O 3 , approx. 6% K 2 O, approx. 3% Na 2 O.
Löbejun porphyry is a weather-resistant hard rock. It has compressive strengths of up to 180 MPa . Since it consists mainly of relatively hard silicate minerals, it is acid-resistant and a polish can be regarded as indefinitely durable. A low porosity makes it highly frost-resistant. The mean density of the rock is 2.63 g / cm³.
use
Löbejun porphyry has been used for almost 500 years in the area around the city of Halle to design facades, as broken stone and masonry stone, and to pave streets and squares. Due to the good mechanical properties and its microstructure properties, numerous streets paved with Löbejun porphyry are still of excellent quality after more than 100 years despite the highest loads. When used as natural stone , Löbejun quartz porphyry is on a par with granite, if not even superior due to the small grain size and thus closer grain interlocking. All common surface treatments of natural stone (rough split, flamed, bush hammered, embossed, sawn, polished) are possible. This results in the following areas of application:
- Window sills, floor and facade panels in the interior and exterior
- Cuboid
- Material for figurative sculptures, tombstones, sculptures, fountains
- Layered masonry in regular and irregular shape
- Armourstones
- Pavers and curbs in various formats, mosaic stones
- Gravity walls
In addition, Löbejun porphyry is also used in the form of aggregates for less noble purposes, including as a raw material for asphalt mixing plants and concrete works as well as for other uses in road, civil engineering, hydraulic engineering and track construction.
Extraction
The first documented mention of the extraction of Löbejun porphyry comes from the year 1518. Since 1992 Löbejun porphyry has been mined in a large industrial quarry immediately west of Löbejün. The raw blocks are obtained by detonating them with highly explosive , modern explosives, with the explosive charge being introduced into large bores. The blocks are then loaded with large open-cast mining equipment and transported for further crushing using cone crushers .
The more gentle extraction of ashlar by hydraulic splitting or blasting using black powder is concentrated on a separate part of the total mining area.
Examples of built-in Löbejun porphyry
- Columns in Magdeburg Cathedral
- Staircases in the inner courtyard of the Wartburg
- All four portals of the Rennsteig Tunnel
- Vertical dividing elements of the State Council building
- Entrance portal Slomanhaus in Hamburg
- Bad Arolsen Castle Square
- Bismarck tower in Spremberg ( List of architectural monuments in Spremberg )
- Bridge cladding between Halle (S.) and Könnern on the federal highway 14
- Sculptures and facade of the Kurt Wabbel Stadium in Halle
- Portal of the Leopoldina building in Halle
- Building facades on the vineyard campus of the Martin Luther University Halle-Wittenberg
- Facade of the Center for European Economic Research , Mannheim
Literature, sources
- Dietrich Franke: Regional Geology East. Geological online reference work for East Germany with around 2500-page encyclopedia (PDF; 19 MB) and separately downloadable maps and tables, etc. a. with a map of the magmatite occurrences (late Variscan granitoids and Rotliegend volcanic rocks) of the Halle-Wittenberg floe (PDF; 532 kB).
- A. Kampe, J. Luge, M. Schwab: The storage conditions in the northern border of the Löbejün porphyry near Halle (Saale) . In: Geology. Vol. 14, No. 1, 1965, pp. 26-46, ISSN 0046-5747 .
- A. Mock, B.-C. Ehling, C. Breitkreuz: Anatomy of a laccolith complex. Geometry and texture of porphyritic rhyolites in the Permocarboniferous Halle Volcanic Complex (Germany). In: New Yearbook of Geology and Palaeontology Treatises. Vol. 237, No. 2, 2005, pp. 211-271, ISSN 0077-7749 .
- Friedrich Müller : INSK compact. Ebner Verlag, Ulm 1997 (2 ring orders in a sturdy slipcase with 320 color plates).
- Siegfried Siegesmund, Karl-Jochen Stein: Löbejüner Porphyry. Natural stone portrait. In: natural stone . Vol. 60, No. 7, 2005, pp. 47-49, (5 figs., 2 tabs.).
Web links
- Facts about the Löbejun porphyry on the website of the company SH-Naturstein, which mines the Löbejun porphyry in the large open-cast mine near Löbejün.
- Löbejün porphyry on the website of the city of Löbejün
Coordinates: 51 ° 37 ′ 32 ″ N , 11 ° 52 ′ 31 ″ E