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Mafic & Felsic
'MAFIC' is a word derived from MAgnesium and Ferric which refers to iron. Mafic rocks are rich in iron and magnesium. Why? Because the minerals from which they form are rich in iron and magnesium. Notice that mafic rocks are also high in density and dark in color and are the rocks found on the right side of 'scheme for igneous rock identifcation' (page 6). The rocks in the blue shaded area are mafic.
"FELSIC' is a term derived from the mineral feldspar. Both kinds of feldspar are rich in the minerals silicon (Si) and aluminum (Al). Felsic rocks are generally light in color and lower in density than mafic rocks. The rocks in the tan shaded area are felsic.
Rocks in the unshaded area in the center are generally neither mafic nor felsic however it is important to understand that this chart is a generalized scheme. Rocks are not made by factories with every piece of granite, for instance, exactly like every other piece of granite. There is great deal of variation in all rocks.
One more point: only rocks can be mafic or felsic. NOT the minerals at the bottom of the chart.
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