|
Andesite is an igneous, volcanic (extrusive) rock, of intermediate composition, with aphanitic to porphyritic texture. Its mineral assembly is usually quartz and plagioclase. Biotite, hornblende and pyroxene are common accessory minerals. Alkali feldspar is absent.
Classification of andesites may be refined according to the most abundant phenocrystal. Example: olivinic andesite, if olivine is the principal accessory mineral.
Andesite can be considered as the extrusive equivalent to plutonic diorite. As diorites, they are characteristic of subduction tectonic environments in active oceanic margins, such as the western coast of South America. Due to this, the name andesite is derived from the Andes mountain range.
See also
|
