Keratophyr
Keratophyr is an igneous rock from the volcanic group , the original mineral composition of which was changed by metamorphic overprinting. The rock has a light, mostly greenish-gray or reddish color and has a dense, chert-like structure. The name was put together by Wilhelm von Gümbel in 1874 from the Greek words keras (κέρας, horn) and phyro (φύρο, to mix).
composition
The main components are alkali feldspars ( albite and orthoclase , often fused together in zones) and quartz . The alkali feldspars often form coarse-grained sprinkles in a fine matrix. The content of dark components is generally low; originally contained minerals of the pyroxene group or amphiboles were converted into stilpnomelane and chlorite during the metamorphosis . Aegirin or Riebeckit can rarely be present. Magnetite , pyrite or hematite can also occur in the fine-grained matrix , with the hematite giving the rock a reddish color.
In the German-speaking area, keratophyres were defined as a metamorphically altered trachyte , usually in common occurrences with Spilites . Internationally, keratophyr is understood to be a bright, metamorphically altered volcanic or dike rock with a trachytic to dacitic composition.
Education and occurrence
The rock occurs worldwide in Paleozoic and Mesozoic mountains in weakly metamorphic areas that were formerly ocean floors. Keratophyre represent acidic volcanic rocks and the spilites associated with them represent former basalts . In Germany, the Devonian deposits in the Lahn-Dill area are known, here there is also a variant that looks more like a diabase and is called Weilburgite . Quartz-rich variants are called quartz keratorphyr .
literature
- Wolfhard Wimmenauer: Petrography of igneous and metamorphic rocks . Enke, Stuttgart 1985, ISBN 3-432-94671-6 , pp. 209-217 .
- Walter Maresch & Olaf Medenbach: Steinbach's natural guide rocks . Mosaik, Munich 1996, ISBN 3-576-10699-5 , p. 112 .
- LJG Schermerhorn: What is keratophyre? . In: Lithos . 6, 1973, pp. 1-11. doi : 10.1016 / 0024-4937 (73) 90076-5 .
Web links
Keratorphy at www.mineralienatlas.de
Individual evidence
- ↑ Hans Murawski: Geological Dictionary. 8th edition, Enke, Stuttgart 1983, p. 111