Mafic and Felsic
The adjective mafic refers to a silicate mineral or rock (magmatic, either intrusive or extrusive) having a chemical composition rich in iron and magnesium and relatively poor in silicium. It corresponds to the older term basic as in basic rock. During crystallization of magma at high temperatures, a magmatic rock tends to concentrate firstly the elements that are easily incorporated into a crystal structure and called “compatible elements,” such as iron and magnesium. Consequently, these rocks contain ferromagnesium minerals such as olivine, pyroxenes, amphiboles, or plagioclase (basalts). Pursuing crystallization of the residual magma, the produced magmatic rocks will tend to concentrate the elements that are not easily incorporated into a crystal structure or “incompatible elements” such as silicon, aluminum, potassium, and sodium. These rocks contain quartz, muscovite, orthoclase, and sodium-rich plagioclase (granites). These minerals are...