Figure F58. Plagioclase phenocryst completely replaced by fine-grained illite (birefringent mineral) and possible halloysite (gray) (interval 193-1188F-14Z-1, 102-105 cm, Unit 41, in cross-polarized light; width of view = 0.7 mm. Photomicrograph ID# 1188F_80; thin section 80).