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The QAPF Diagram
The chapter Quartz as a Rock-Forming Mineral introduced the QAPF diagram as a means to visualize and memorize the classification of igneous rocks based on their content of the minerals quartz, alkali-feldspar, plagioclase, and foids.This chapter serves to fully assign rock types to all fields in the diagram.
Fig.1.1: QAPF Diagram for Igneous Rocks
The QAPF diagrams for plutonic and volcanic rocks look almost the same (Fig.1.1), except that field 15 is subdivided into 3 fields in volcanic rocks, and rocks no rocks have been assigned to fields 1 and 1a of the volcanic QAPF diagram.
There are 20 "basic names", that have been marked bold in the table, and many others derived from it: for example there is:
- syenite
- quartz-bearing syenite
- foid-bearing syenite
- alkali-feldspar syenite
and so on.
That the "basic names" names have been marked bold bears no significance on the abundance of those rocks in nature, it is simply done to help memorizing the names.
| Plutonic Rocks | Volcanic Rocks | |
|
1 1a 2 3 4 5 6 6a 6b 7 7a 7b 8 8a 8b 9 9a 9b 10 10a 10b 11 12 13 14 15 15a 15b 15c |
Quartz-Rich Granitoid Quartzolite Alkali-Feldspar Granite Granite Granodiorite Tonalite Alkali-Feldspar Syenite Quartz-Bearing Alkali-Feldspar Syenite Foid-Bearing Alkali-Feldspar Syenite Syenite Quartz-Bearing Syenite Foid-Bearing Syenite Monzonite Quartz-Monzonite Foid-Monzonite Monzodiorite / Monzogabbro Quartz-Monzodiorite / Quartz-Monzogabbro Foid-Monzodiorite / Foid-Monzogabbro Diorite / Gabbro / Anorthosite Quartz-Diorite / Quartz-Gabbro Foid-Bearing Diorite / Foid-Bearing Gabbro Foid-Syenite (Foyaite) Foid-Monzosyenite Foid-Monzodiorite (Essexite) Foid-Diorite Foidolite - - - |
- - Alkali-Feldspar Rhyolite Rhyolite Dacite Plagidacite Alkali-Feldspar Trachyte Quartz-Bearing Alkali-Feldspar Trachyte Foid-Bearing Alkali-Feldspar Trachyte Trachyte Quartz-Trachyte Foid-Bearing Trachyte Latite Quartz-Latite Foid-Bearing Latite Andesite Quartz-Bearing Andesite Foid-Bearing Andesite Basalt Quartz-Bearing Basalt Foid-Bearing Basalt Phonolite Tephritic Phonolite Phonolitic Tephrite / Phonolitic Basanite Tephrite / Basanite - Phonolitic Foidite Tephritic Foidite Foidite |
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