Figure F54. Photomicrograph of a pervasively silicified volcanic rock, showing quartz amygdules, granules, and microcrystalline silica-clay alteration of the formerly glassy portion of the microlitic groundmass. Remnant plagioclase microlites are visible (interval 193-1189A-12R-1, 67-69 cm, Unit 20, in cross-polarized light; width of view = 1.4 mm. Photomicrograph ID# 1189A

Figure F54. Photomicrograph of a pervasively silicified volcanic rock, showing quartz amygdules, granules, and microcrystalline silica-clay alteration of the formerly glassy portion of the microlitic groundmass. Remnant plagioclase microlites are visible (interval 193-1189A-12R-1, 67-69 cm, Unit 20, in cross-polarized light; width of view = 1.4 mm. Photomicrograph ID# 1189A_85; thin section 41).