Basic rock
A basic rock is a magmatic rock having a SiO 2 content of 45-52 weight percent . A rock with a lower SiO 2 content is called ultrabasic rock , and one with a higher content is called intermediate (52 to 63%) or acidic rock (more than 63%). Metamorphic overprinted basic rocks are summarized under the name metabasite .
Characteristics
A basic rock consists of potassium- poor feldspars ( plagioclase ) and often from mafic minerals such as pyroxene and amphibole . Due to the content of 45 to 52%, a basic rock can either be SiO 2 - supersaturated or - undersaturated. In the first case it contains free SiO 2 in the form of quartz or cristobalite , in the second case it contains olivine or minerals from the group of foids instead . Although not exactly synonymous, the terms basic rock , referring to the relatively low SiO 2 content of the rock, and mafic rock , referring to the relatively high proportion of mafic minerals , are often used synonymously, since one is usually associated with the other . Correspondingly, basic rocks often have a dark color.
Typical representatives of the group of basic rocks are gabbro (a plutonite ), dolerite ( sub- volcanic rock ) and basalt ( volcanic rock ).
literature
- RW Le Maitre et al .: Igneous Rocks: A Classification and Glossary of Terms: Recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks. 252 pp., Cambridge University Press 2005. ISBN 978-0-521-61948-6