What is not one of the factors that are used to identify and distinguish ranks of global cities?10/7/2023 ![]() ![]() ![]() Figure 3.16 A simplified classification diagram for igneous rocks based on their mineral compositions To be more specific, felsic rocks typically have biotite and/or amphibole intermediate rocks have amphibole and, in some cases, pyroxene and mafic rocks have pyroxene and, in some cases, olivine. Intermediate rocks have between 20% and 50% ferromagnesian silicates, and mafic rocks have 50% to 100% ferromagnesian silicates. At the same time, it’s quite difficult to estimate the proportions of minerals in a rock.īased on the position of the red line in Figure 3.16, it is evident that felsic rocks can have about 1% to 20% ferromagnesian silicates (the red line intersects the left side of the felsic zone 1% of the distance from the top of the diagram, and it intersects the right side of the felsic zone 20% of the distance from the top). That’s relatively easy in most igneous rocks because the ferromagnesian minerals are clearly darker than the others. ![]() In classifying intrusive igneous rocks, the first thing to consider is the percentage of ferromagnesian silicates. An important feature to note on this diagram is the red line separating the non-ferromagnesian silicates in the lower left (K-feldspar, quartz, and plagioclase feldspar) from the ferromagnesian silicates in the upper right (biotite, amphibole, pyroxene, and olivine). The diagram in Figure 3.16 can be used to help classify igneous rocks by their mineral composition. As has already been described, igneous rocks are classified into four categories, based on either their chemistry or their mineral composition: felsic, intermediate, mafic, and ultramafic. ![]()
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