Fig. 18. Microcline (gray; grid-twinned; bottom) penetrates and replaces plagioclase (white) along grain boundaries between plagioclase crystals. Plagioclase in wartlike myrmekite is optically continuous with the quartz-free plagioclase. The microcline penetrates the myrmekite (upper right and lower left) and surrounds tiny islands of plagioclase that are optically continuous with the larger plagioclase grain (white). Echo Lake granodiorite, south shore of Lower Echo Lake, 1.6 km south of Flagpole Peak. Thin section 58 from Loomis collection.