To use all functions of this page, please activate cookies in your browser.
With an accout for my.chemeurope.com you can always see everything at a glance – and you can configure your own website and individual newsletter.
- My watch list
- My saved searches
- My saved topics
- My newsletter
A QAPF diagram is a double triangle diagram which is used to classify igneous rocks based on mineralogic composition. The acronym, QAPF, stands for "Quartz, Alkali feldspar, Plagioclase, Feldspathoid (Foid)". These are the mineral groups used for classification in QAPF diagram. Q, A, P and F percentages are normalized (recalculated so that their sum is 100%).
Additional recommended knowledge
QAPF diagrams are mostly used to classify plutonic rocks (phaneritic rocks) (Figure 1), but are also used to classify volcanic rocks (Figure 2) if modal mineralogical compositions have been determined. QAPF diagrams are not used to classify pyroclastic rocks or volcanic rocks if modal mineralogical composition is not determined, instead the TAS classification (Total-Alkali-Silica) is used. TAS is also used if volcanic rock contains volcanic glass (such as obsidian). QAPF diagrams are also not used if mafic minerals make up more than 90% of the rock composition (for example: peridotites and pyroxenites).
An exact name can be given only if the mineralogical composition is known, which cannot be determined in the field. Therefore, provisional or field classifications (Figures 3 and 4) are used, which are simplified versions of Figures 1 and 2.
QAPF diagrams were created by the International Union of Geological Sciences (IUGS): Subcommission on the Systematics of Igneous Rocks. The diagrams are accepted by geologists worldwide as a classification of igneous, especially plutonic rocks.
Contrary to copyright assertions, the following graphics are almost certainly not available for free public distribution. The originals are in Igneous Rocks: A classification and Glossary of Terms, 2nd Edition; 2002; R.W. Le Maitre editor; Cambridge University Press.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "QAPF_diagram". A list of authors is available in Wikipedia.|