Figure F53. Coarse-grained, bladed anhydrite filling the center of a quartz-pyrite vein in a bleached volcanic rock. Silica-pyrite ± anhydrite veins with bleached alteration halos are abundant in bleached volcanic rocks and are interpreted to be intimately related to the alteration. Anhydrite, where present, is invariably the last phase to precipitate in these veins (interval 193-1189A-3R-1, 70-73 cm, Unit 9, in cross-polarized light; width of view = 2.75 mm. Photomicrograph ID# 1189A

Figure F53. Coarse-grained, bladed anhydrite filling the center of a quartz-pyrite vein in a bleached volcanic rock. Silica-pyrite ± anhydrite veins with bleached alteration halos are abundant in bleached volcanic rocks and are interpreted to be intimately related to the alteration. Anhydrite, where present, is invariably the last phase to precipitate in these veins (interval 193-1189A-3R-1, 70-73 cm, Unit 9, in cross-polarized light; width of view = 2.75 mm. Photomicrograph ID# 1189A_20; thin section 30).