ANDESINE  , a member of the

group of minerals known as plagioclase felspars, occupying a position in the isomorphous series about midway between albite (NaAISi3O8) and anorthite (CaAl2Si2O3); its chemical composition and physical characters are therefore intermediate between those of the two extremes of the series . Distinctly developed crystals or crystallized specimens are rarely met with, the mineral usually occurring as embedded crystals and grains in the igneous and gneissic rocks, of which it forms a component part . It occurs, for example, in the andesite of the Andes, from whence it derives its name .