Fig. 36. Interstitial K-feldspar (black; center) penetrates and replaces albite-twinned plagioclase (black and white; left side) in irregular veins. The K-feldspar also replaces plagioclase along the grain boundary between quartz (light gray; bottom) and plagioclase (white; lower right side). Biotite (brown). From the Glen Alpine granodiorite, 100 meters from eastern border of the pluton.