Fig. 1. This photo shows a cathodoluminescent image of a normally zoned plagioclase crystal where the host diorite is only slightly deformed. Relatively calcic cores luminesce with pale yellow or yellow-green colors. Toward the rim where it is more sodic, the color becomes beige, then purplish. Not seen in cross-polarized light but apparent under cathodoluminescence is the fact that the plagioclase crystal is slightly fractured. Electron-microprobe studies show that along the fractures calcium has been lost, producing veins of more-sodic residual plagioclase (gray purple) through the crystal (bottom of central crystal and extending into the crystal at top}. Locally, tiny islands of K-feldspar (light or bright blue) occur in the center of the veins. Electron microprobe studies show that cores in an unaltered zoned plagioclase grain are An_37-39 and rims An_17-20. All Si in the analyses fits into the plagioclase crystal structure.