Fig. 19. Albite-twinned plagioclase (dark gray) is bordered by myrmekite and projects into a microcline megacryst (grayish white). Plagioclase of the myrmekite is optically continuous with the larger plagioclase crystal. Optically parallel islands of the plagioclase (gray; right side, center) are enclosed in the microcline (grayish white). Biotite (brown). Sericite alteration (blue).