Acidic rock oracid rock refers to the chemical composition ofigneous rocks that has 63% wt% SiO2 content.[1] Rocks described as acidic usually contain more than 20% of freequartz.[2] Typical acidic rocks aregranite orrhyolite.
The term is used in chemical classification ofigneous rock based on the content ofsilica (SiO2). Because chemical analyzes are not always available, especially during the fieldwork, classification based on the mineral (modal) composition is more often used (dividing the igneous rocks intofelsic/leucocratic,mafic/melanocratic andultramafic).
The term "silicic", widely used in South America, has wider meaning, however, is often used as broadly synonymous with "acidic".[3]
Terms describing composition of igneous rocks as acidic orbasic evolved during the 19th century. It was based on the idea that high silica rocks areacidic and on the contrary the rocks with low silica content arebasic. Although this idea is erroneous in a chemical sense (acidic rocks don't have lowpH), both terms are used today.[4]
See also
editReferences
edit- ^Maitre, R. W. Le, Streckeisen, A., Zanettin, B., Bas, M. J. Le, Bonin, B., Bateman, P., 2002: 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, 252 pp. ISBN 978-0-521-66215-4.
- ^Mannell, F. P., 1913: A manual of petrology. Chapmann & Hall, Covent Garden, p. 118
- ^Gill, R., 2010: Igneous rocks and processes: a practical guide. John Wiley & Sons, Chichester, ISBN 978-1-4443-3065-6 p. 8
- ^Camp, Vic (2000)."Historical note on rock terminology (basic/acidic vs. mafic/felsic)".How Volcanoes Work. Department of Geological Sciences, San Diego State University. Retrieved22 June 2022.
