Fig. 8. Carlsbad- and albite-twinned, zoned plagioclase in Bonsall tonalite. Relatively calcic core (black, altered to sericite) of plagioclase is surrounded by a broad, relatively sodic rim. Plagioclase rim has irregular or rectangular islands of K-feldspar (black, or gray-white gingham-pattern). Biotite (brown); muscovite (blue and yellow).