Figure F17 (continued). E. Fragmentation of a larger pumice clast to generate smaller pumice fragments in the matrix. F. Internal texture in a pumice clast showing changes in orientation of tube vesicles and incipient alteration to pale green clay minerals. Photomicrographs A-C are from Sample 183-1138A-78R-4, 23-26 cm (in plane-polarized light; field of view = 1.4 mm). Photomicrographs D-F are from Sample 183-1138A-78R-3, 50-54 cm (in plane-polarized light; field of view = 1.4 mm).