Figure F21. Digital photomicrograph (plane-polarized light) of a subrounded fragment of hornblende and plagioclase-phyric basalt with a glassy matrix (center) within a medium-grained volcaniclastic sandstone. Surrounding grains include fresh crystals of hornblende, plagioclase, quartz, and glass shards. Planktonic foraminifers rarely occur (Sample 180-1118A-67R-4, 73-74 cm).