Fig. 12. Photomicrograph (100x). Unaltered sodic plagioclase core (right side) is bordered by two narrow zones of altered plagioclase (brownish), showing progressive early stages of losing sodium and being replaced by calcium and aluminum. Farther to the left in the center (black) is a broad zone containing myrmekite and tracs of amphibole laths. Against the myrmekite zone (left side) is a thin unaltered plagioclase rind, outlining the shape of the former shape of the plagioclase crystal. Farthest to the left is the host, fine-grained, mafic tonalite containing plagioclase, biotite, and hornblende.