Figure F79. Photomicrograph of Sample 185-801C-16R-5, 107-110 cm. Glass, clay, and calcite are labeled. A 100-µm-long lath of plagioclase (white) is near the bottom of the picture. The glass at the contact with the clay is opaque black. Clay is gray to light brown, and the white region in the upper left is calcite. The crack from the center bottom to the upper right was probably created during the manufacture of the thin section. Photo was taken with a 20× objective lens in plane-polarized light.