ANDESINE (named by W. H. Abich in allusion to its oc currence in the Andes mountains), a mineral of the plagioclase group of felspars (q.v.) and occupying a position about midway in the isomorphous series, albite-anorthite. In petrology the name is arbitrarily restricted to solid solutions between and Andesine is an essential constituent of the inter mediate igneous rocks, as diorite, porphyrite and andesite.