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Geology is the Way

Classification of gabbros

Gabbroid rocks are a large family of plutonic rocks that contain almost exclusively plagioclase as the only felsic mineral, hence plotting close to the P vertex of the QAPF classification diagram (quartz < 5% and plagioclase > 90% feldspars). The relatively simple classification through the QAPF diagram hides, however, the true complexity of these rocks, which may contain variable proportion of plagioclase with variable calcium- to sodium-rich composition and a wide range of different femic minerals, including pyroxene (ortho- and clino-), olivine, and hornblende.