Figure 12. Photomicrograph in cross-polarized light of a fresh plagioclase phenocryst set in groundmass containing 35 vol% fresh plagioclase microlites, 35 vol% quartz, 25 vol% brown clay, and 5 vol% pyrite (Sample 193-1188F-31Z-1, 1–3 cm; field of view = 2.75 mm).