Plagioclase

Plagioclase, the collective name for those varieties of felspar (q.v.) that crystallise in the Anorthic system, including rnicrocline, a potash felspar, albitc, or soda felspar, anorthite, or lime felspar, and the intermediate forms oligoclase, or soda-lime felspar, andesine, or soda and lime felspar, and lahradorite, or lime-soda felspar, which Tchermak regards as only isomorphous twin combinations of albite and anorthite.