Because most igneous rocks are composed of silicate minerals, the earliest chemical classification used was one based on weight percentage of SiO2 in the rock. This led to the subdivision of igneous rocks into four categories—acid(ic), intermediate, basic, and ultrabasic. Over the years, different authors have varied slightly in the limits of SiO2 percentage for the four groups, but many petrologists designate igneous rocks with ≫66% SiO2 as acidic, 52–66% SiO2 as intermediate, 45–52% SiO2 as basic, and ≪45+ SiO2 as ultrabasic (≫65%, 65–55%, 55–45% and ≪45% are also used). Some authors use the term subsilicic and others use the term mafic synonymously with basic although mafic is mainly used in relation to dark-colored Mg–Fe minerals or rocks rich in these minerals. The terms acidic and basic may also be used in a relative manner, e.g., to indicate that one rock is more basic than another even though the rock referred to may contain more than 52% SiO2.
With chemical analyses available...
This is a preview of subscription content, log in via an institution to check access.
Access this chapter
Tax calculation will be finalised at checkout
Purchases are for personal use only
Bibliography
Clark, R. H., 1956, A petrological study of the Arthur's Seat volcano, Trans. R. Soc. Edinburgh 63, 37–70.
Hatch, F. H., A. K. Wells, and M. K. Wells, 1972, The Petrology of the Igneous Rocks, 13th edn. London: Murby.
Hess, H. H. and A. Poldervaart, eds., 1967, 1968, Basalts. The Poldervaart Treatise on Rocks of Basaltic Composition, Vols. 1, 2. New York: Wiley Interscience.
Hughes, C. J., 1982, Igneous Petrology: Developments in Petrology Series No. 7. Amsterdam: Elsevier.
Wilkinson, J. F. G., 1967, The petrography of basaltic rocks, in H. H. Hess and A. Poldervaart, eds., Basalts, Vol. 1, New York: Wiley Interscience, 163–214.
Cross-references
Rights and permissions
Copyright information
© 1989 Van Nostrand Reinhold
About this entry
Cite this entry
Whyte, F. (1989). Basic igneous rocks . In: Petrology. Encyclopedia of Earth Science. Springer, Boston, MA. https://doi.org/10.1007/0-387-30845-8_25
Download citation
DOI: https://doi.org/10.1007/0-387-30845-8_25
Publisher Name: Springer, Boston, MA
Print ISBN: 978-0-442-20623-9
Online ISBN: 978-0-387-30845-6
eBook Packages: Springer Book Archive