Figure F13. Digital photomicrograph (plane-polarized light) of a well-rounded clast of porphyritic basalt with a glassy matrix and phenocrysts of plagioclase and hornblende surrounded by rounded basic volcanic clasts, feldspar, quartz, and calcite; note benthic foraminifer near the top of the field of view (interval 180-1116A-8R-1, 37-40 cm).