Fig. 13a. A scanning-electron photomicrograph that shows celsian islands (ce, white) in altered plagioclase partly replaced by K-feldspar (magnification: 1600x). The plagioclase (pl, dark gray) is full of holes (black) with angular boundaries parallel to the plagioclase crystal lattice, and many holes are bordered by concentrations of K (lighter gray, incipient K-feldspar, kf). In some places the celsian occurs on hole walls adjacent to the K concentrations.