Leucocrates rock

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Granite (left) is a typical leucocrates rock (here: Fjaeregranit , Proterozoic of southern Norway).

Leucocrate rocks (from ancient Greek λευκός leukós , German 'white' ), also called leuco rocks for short , are igneous rocks with a relatively light hue. The reason for this is that the rock has a relatively low volume fraction of dark mafic minerals ( color index M ′ ).

In a narrower sense, the attribute “leucocrates” applies to rocks with M ′ between 10 and 35. Rocks with M ′ <10 are called hololeucocrates and rocks with M ′ between 35 and 65 are called mesocrat or mesotype . Typical leucocrate rocks are e.g. B. granite , rhyolite or anorthosite .

In addition, it is common for igneous rocks to prefix a rock name with the prefix leuco if the rock in question is lighter than the average rock of the same rock family. The decisive factor here is the average value for M ′ within the rock family under consideration. For example, in a leukogranite M ′ is so low (<5) that it would generally be classified as a hololeucocrate rock, while M ′ in a leukogabbro is significantly higher with <35.

literature

  • RW Le Maitre (Eds.), A. Fahrtisen, B. Zanettin, MJ Le Bas, B. Bonin, P. Bateman, G. Bellieni, A. Dudek, S. Efermova, J. Keller, J. Lameyre, PA Sabine , R. Schmid, H. Sørensen, AR Woolley: Igneous Rocks: A Classification and Glossary of Terms. Recommendations of the International Union of Geological Sciences, Subcommission on the Systematics of Igneous Rocks. Cambridge University Press, 2002, ISBN 978-0-521-66215-4
  • Walter Schumann: The new BLV stone and mineral guide . 6th edition, BLV Verlags GmbH, Munich (2002), ISBN 3-405-16441-9
  • Wolfhardt Wimmenauer: Petrography of igneous and metamorphic rocks. Enke-Verlag, Stuttgart 1985, p. 106 ff., ISBN 3-432-94671-6

Notes and individual references

  1. ↑ Usually, a volume fraction is always given in percent. However, if the volume fraction of dark Mafite is specified as the color index M ′, the percentage symbol is omitted.
  2. ^ Volkmar Trommsdorff, Volker Dietrich: Fundamentals of Earth Sciences: Lecture for the University and ETH Zurich. 6. revised Ed., Vdf Hochschulverlag AG at the ETH Zurich, Zurich 1999, ISBN 3-7281-2078-2 , p. 57.

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