Figure F21. A. Photomicrograph of a zoned and twinned plagioclase grain in a sandstone from Unit II. The dusky inner part of the grain represents the slightly altered, calcic-rich core of the feldspar, whereas the fresh margin is sodium rich. Arrows point to incipient diagenetic feldspar overgrowth in optical continuity with the detrital grain (thin section from Sample 195-1201D-14R-1, 9-11 cm [205.39 mbsf]) (cross-polarized light). B. Photomicrograph of authigenic prismatic lathes of phillipsite and pore-lining clay rim in a vitrophyre vesicle. The clay rim consists of small flakes of expandable clay minerals that grew perpendicular to the detrital substrate into the pore space (thin section from Sample 195-1201B-8X-2, 22-24 cm [53.62 mbsf]) (plane-polarized light).

Figure F21. A. Photomicrograph of a zoned and twinned plagioclase grain in a sandstone from Unit II. The dusky inner part of the grain represents the slightly altered, calcic-rich core of the feldspar, whereas the fresh margin is sodium rich. Arrows point to incipient diagenetic feldspar overgrowth in optical continuity with the detrital grain (thin section from Sample 195-1201D-14R-1, 9-11 cm [205.39 mbsf]) (cross-polarized light). B. Photomicrograph of authigenic prismatic lathes of phillipsite and pore-lining clay rim in a vitrophyre vesicle. The clay rim consists of small flakes of expandable clay minerals that grew perpendicular to the detrital substrate into the pore space (thin section from Sample 195-1201B-8X-2, 22-24 cm [53.62 mbsf]) (plane-polarized light).