Theralith
Theralith (also Theralite ) is the name for a plutonic rock from the group of foid-bearing gabbros . The name is derived from an occurrence on the island of Thera in the Aegean Sea . It was first described by Karl Heinrich Rosenbusch in 1887.
Mineral inventory and rock description
The mineral inventory includes plagioclase ( andesine and labradorite ), more than 10% foide (mostly nepheline ), augite , olivine and, in small amounts, biotite , up to a maximum of 10% alkali feldspar and alkali amphibole . Apatite , titanite and sulphidic ore minerals occur as accessory components, but never quartz . With this composition, Theraliths belong to the group of gabbroids . If the total content of dark minerals is less than 30%, the prefix Leuko is placed in front of the rock name, if the content is over 70% the prefix Mela . Theraliths are often coarse-grained and have a uniform grain structure .
Origin and occurrence
As strongly silicon- undersaturated rocks, Theraliths never occur in tectonic active zones like collision orogens . They are mainly found as smaller occurrences in deep fault zones or trenches where material from the earth's mantle can penetrate. In addition to the type locality on the island of Thera, this rock is found on the Kola Peninsula and in the Messum crater in Namibia . In Germany there is a small deposit in the Upper Rhine Graben at the Kaiserstuhl .
The volcanic equivalent of theralite is basanite .
literature
- Walter Maresch & Olaf Medenbach: Rocks . Mosaik-Verlag, Munich 1996, ISBN 3-576-10699-5 , pp. 80 .
- Wolfhard Wimmenauer: Petrography of igneous rocks . Enke, Stuttgart 1985, ISBN 3-432-94671-6 , pp. 126-130 .
Web links
- Meyers Großes Konversations-Lexikon, Volume 19. Leipzig 1909, p. 473.
- Theralith at www.mineralienatlas.de , accessed on May 6, 2013