md`# AFM Diagram of Igneous Petrology *Not to be confused with the AFM diagram of metamorphic petrology* The AFM diagram is a ternary plot used to show the relative proportions of the oxides of alkalis (A), iron (F), and magnesium (M) in igneous rocks. The components of the diagram are thus **A** (Alkalis: Na₂O + K₂O), **F** (FeO & Fe₂0₃), and **M** (MgO). This diagram includes the boundaries between the "tholeiitic" and "calc-alkaline" or "olivine" fields (heavy lines) as proposed Irvine and Baragar (1971). In the classification of Irvine and Baragar the three main series are : 1. The tholeiitic basalt 2. Calc-alkali 3. Alkali olivine basalt series ## Sources * [Tulane University - Igneous Rocks and Plate Tectonics](http://www.tulane.edu/~sanelson/eens211/igneous_rocks_plate_tectonics.htm) - Prof. Stephen A. Nelson * [Wikipedia - Igneous Rocks](https://en.wikipedia.org/wiki/Igneous_rock#Chemical_classification_and_petrology) ` //* [*A Dictionary of Geology and Earth Sciences*](https://www.oxfordreference.com/view/10.1093/oi/authority.20110803095354650) - Michael Allaby, Oxford University Press, 2013, ISBN-139780199653065 // Triangular diagrams are often used to show the compositional ranges in minerals // The AFM diagram is a ternary plot used to show how metamorphic mineral assemblages vary as a function of rock composition within one metamorphic facies. // Besides SiO₂, the five most abundant oxides found in metamorphic rocks are Al₂O₃, CaO, FeO, MgO, and K₂O. // The components of the diagram are thus Alkalis (Na₂O + K₂O ) **A** , **F** (*FeO*), and **M** (*MgO*). // A–alkali (sodium and potassium) oxides, F–iron oxides, M–magnesium oxide, BT–tholeiitic basalt, FB–ferro-basalt, ABT–tholeiitic basaltic andesite, AT–tholeiitic andesite, D–dacite, R–rhyolite, B–basalt, AB–basaltic andesite, A–andesite; dashed line–boundary between tholeiitic and calc-alkaline compositions. // (*Al₂O₃*)