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:For the extinct cephalopod genus, see Andesites.Andesite (c-eniconˈændəsaɪt) is an extrusive igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. In a general sense, it is the intermediate type between basalt and dacite. The mineral assemblage is typically dominated by plagioclase plus pyroxene and/or hornblende. Magnetite, zircon, apatite, ilmenite, biotite, and garnet are common accessory minerals. Alkali feldspar may be present in minor amounts. The quartz-feldspar abundances in andesite and other volcanic rocks are illustrated in QAPF diagrams. Relative alkali and silica contents are illustrated in TAS diagrams.
Classification of andesites may be refined according to the most abundant phenocryst. Example: hornblende-phyric andesite, if hornblende is the principal accessory mineral.
Andesite can be considered as the extrusive equivalent of plutonic diorite. Andesites are characteristic of subduction zones, such as the western margin of South America. The name andesite is derived from the Andes mountain range.
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