Figure F23. Photomicrographs of advanced stage of diagenesis in sandstones from the middle to lower part of Unit II. The sample exhibits vesicles in sideromelane with pore-lining clay rims from an earlier stage of diagenesis. Later, the vitric groundmass was completely replaced by sparry, partly poikilotopic zeolite, including needles of another zeolite generation. The zeolites might be members of the heulandite-clinoptilolite and analcime-wairakite solid solution series (thin section from Sample 195-1201D-30R-6, 114-116 cm [367.74 mbsf]) A. Plane-polarized light. B. Cross-polarized light.

Figure F23. Photomicrographs of advanced stage of diagenesis in sandstones from the middle to lower part of Unit II. The sample exhibits vesicles in sideromelane with pore-lining clay rims from an earlier stage of diagenesis. Later, the vitric groundmass was completely replaced by sparry, partly poikilotopic zeolite, including needles of another zeolite generation. The zeolites might be members of the heulandite-clinoptilolite and analcime-wairakite solid solution series (thin section from Sample 195-1201D-30R-6, 114-116 cm [367.74 mbsf]) A. Plane-polarized light. B. Cross-polarized light.