Limburgite

Limburgite from Limberg am Kaiserstuhl

As limburgite a is basanite (a basaltic volcanic rock ) with a vitreous matrix and porphyritic structure referred to. The name is derived from its type locality , the Limberg or Limburg near Sasbach am Kaiserstuhl in Baden-Württemberg . It was introduced by the geologist Karl Heinrich Rosenbusch in 1872.

Rock description

Limburgite under the microscope

Limburgite (thin section, LPL): crystals of olivine, pyroxene and magnetite in a glassy, dark brown matrix (Hohenzell, southern Vogelsberg)

Limburgite (thin section, XPL): Glassy components remain dark

In general, limburgites usually consist of a reddish-brown or gray-brown glassy or (after devitrification ) microcrystalline matrix in which there are fragments of olivine and clinopyroxene . As the number of sprinkles decreases, the rock can gradually transition into a basaltic rock glass, mostly in the edge areas of a former lava flow, which have cooled down faster than the rest.

In the limburgite from Sasbach, the olivine is no more than 3 mm in size and is mostly only present in weathered form, either as yellowish limonite or as red hematite . The clinopyroxene is a black Ti - Augite of up to 1 cm in size, which, thanks to its idiomorphic growth, often has the characteristic octagonal cross-sections and two head surfaces. Twins and multiple adhesions are often observed. In bladder cavities, which are very common in the rock, various minerals have formed after the rock formation through transformation processes, e.g. B. zeolites ( faujasite , philipsite, etc.), calcite , aragonite and opal ( hyalite ). These secondary minerals make Limburgite interesting for mineral collectors.

Occurrence

Limburgites usually occur in association with other volcanic alkali rocks , such as alkali basalts , basanites or tephrites . In Germany, well-known sites are outside the Kaiserstuhl, for example in the Vogelsberg , the Rhön or the Hohe Meißner .

The locality on the Limberg

On the north-western edge of the Kaiserstuhl, several limburgitic lava flows are exposed in seven quarries (I-VII) , some of which are formed as block or Aa lava . They erupted from a side crater of the volcano around 16 million years ago during the late phase of the Kaiserstuhl development in the Miocene . The limburgite flows together with an olivine- nephelinite- lava flow and the remains of a cinder cone ( red wall in quarry VII) form the so-called Limberg-Lützelberg complex. In the largest outcrop, Quarry I, two limburgite sequences are separated from one another by a thin layer of tuffite and lake sediment .

use

Due to the close proximity of the limburgite deposit from Sasbach to the Rhine , the rock was broken in several quarries in the 19th century as building material for straightening the Rhine . Today the limburgite at this site no longer has any economic significance.

literature

Wolfhard Wimmenauer : The igneous rocks . In: Geological State Office in Baden-Württemberg (Hrsg.): Geological excursion map of the Kaiserstuhl. 1: 25000. Explanations . State Surveying Office Baden-Württemberg, Stuttgart 1959.
Walter Maresch, Olaf Medenbach: Rocks . With the collaboration of Hans Dieter Trochim. Edited by Gunter Steinbach . New, edited special edition. Mosaik-Verlag, Munich 1987, ISBN 3-576-10699-5 ( Steinbach's natural guide ).

Individual evidence

↑ Wolfhard Wimmenauer: Geological map of Bade-Württemberg 1: 25,000, sheet Kaiserstuhl . Ed .: State Office for Geology, Raw Materials and Mining Baden-Württemberg. 5th edition. Freiburg 2003, p. 52 .

[1] Wolfhard Wimmenauer: Geological map of Bade-Württemberg 1: 25,000, sheet Kaiserstuhl . Ed .: State Office for Geology, Raw Materials and Mining Baden-Württemberg. 5th edition. Freiburg 2003, p. 52 .