Löbejun porphyry

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Sawn handpiece made of Löbejun porphyry with a polished surface.

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

Handpiece sawn in shape from Löbejun porphyry with a flamed surface

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

View into the Löbejün porphyry quarry

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

The vertical red elements in the facade of the State Council building in Berlin are made of Löbejun porphyry.

Literature, sources

Web links

Coordinates: 51 ° 37 ′ 32 ″  N , 11 ° 52 ′ 31 ″  E