The IUGS systematics of igneous rocks

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doi: 10.1144/gsjgs.148.5.0825
Authors:Le Bas, M. J.; Streckeisen, A. L.
Author Affiliations:Primary:
University of Leicester, Department of Geology, Leicester, United Kingdom
Volume Title:Journal of the Geological Society of London
Source:Journal of the Geological Society of London, Vol.148 (Part 5), p.825-833. Publisher: Geological Society of London, London, United Kingdom. ISSN: 0016-7649
Publication Date:1991
Note:In English. 24 refs.; illus., incl. 2 tables
Summary:The principles established for the construction of a sustainable classification of igneous rocks are: 1) use descriptive attributes, 2) use actual properties, 3) ensure suitability for all geologists, 4) use current terminology, 5) define boundaries of rock species, 6) keep it simple to apply, 7) follow natural reactions, 8) use modal mineralogy, 9) if mode not feasible, use chemistry, 10) follow terminology of other IUGS bodies. The classification separates and individually classifies the pyroclastic, carbonatitic, melilitic, lamprophyric and charnockitic rocks before entering the main QAPF classification for plutonic and volcanic rocks, which is based on the modal proportions of quartz (Q), alkali feldspar (A), plagioclase (P) and feldspathoids (F). Rocks with mafic content >90% have their own classification. If the mineral mode cannot be determined, e.g. for volcanic rocks, then a chemical classification of total alkalis vs silica (TAS) is used. The details of the individual classifications are not given but can be found in the book. [R.A.H.]
Subjects:Chemical composition; Classification; Igneous rocks; IUGS; Nomenclature; Plutonic rocks; Ultramafics; Volcanic rocks
Abstract Numbers:92M/0966
Record ID:1995041857
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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