GEOL 212 Lecture Notes - Lecture 46: Olivine, Gabbro, Pyroxene
26 Dec 2017
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Document Summary
Chemical and mineral composition: the actual names of igneous rock types reflect both: composition, texture and crystal size. The chart below gives a taxonomy of the most common igneous rocks. Its x axis shows the percentage of silica in the rock, the y axis shows the relative abundance of different minerals in the rock. Remember, for each composition there are intrusive and extrusive versions. For example, we see that granite might have 70% silica and be composed of 50% orthoclase, 25% quartz, and 25% plagioclase, muscovite, biotite, and amphibole. Felsic: high quantities of orthoclase and quartz, small amounts of plagioclase, muscovite, biotite, and amphibole: granite (intrusive). Common component of continental crust: rhyolite (extrusive). Common component of continental crust: andesite (extrusive). Tends to erupt on continents, often above subducting plates. Mafic (mafic = ma + fe): high quantities of olivine and pyroxene, smaller amounts of plagioclase: gabbro (intrusive). Major component of oceanic crust: basalt (extrusive).
