Figure F56. Photomicrographs of poikiloblastic silicification in Unit 15. All images are taken from interval 193-1189A-8R-1, 42-44 cm. A. Poikiloblastic quartz overgrowth on a possible quartz phenocryst. The overgrowth is optically continuous with the crystal (in cross-polarized light; width of view = 1.4 mm [Photomicrograph ID# 1189A_49; thin section 38]). B. Poikiloblastic quartz overgrowth on a quartz-pyrite amygdule (in cross-polarized light; width of view = 0.7 mm [Photomicrograph ID# 1189A_50; thin section 38]). C. Narrow quartz-pyrite vein with a patchily developed poikiloblastic quartz alteration halo. The poikiloblastic quartz is optically continuous with quartz grains in adjacent segments of the vein (in cross-polarized light; width of view = 1.4 mm [Photomicrograph ID# 1189A_52; thin section 38]). D. Hairline quartz vein with relatively coarse euhedral pyrite (bluish cream color). Poikiloblastic quartz alteration is developed in the groundmass of the rock in this field of view (in simultaneous plane-polarized transmitted and reflected light; width of view = 1.4 mm [Photomicrograph ID# 1189A

Figure F56. Photomicrographs of poikiloblastic silicification in Unit 15. All images are taken from interval 193-1189A-8R-1, 42-44 cm. A. Poikiloblastic quartz overgrowth on a possible quartz phenocryst. The overgrowth is optically continuous with the crystal (in cross-polarized light; width of view = 1.4 mm [Photomicrograph ID# 1189A_49; thin section 38]). B. Poikiloblastic quartz overgrowth on a quartz-pyrite amygdule (in cross-polarized light; width of view = 0.7 mm [Photomicrograph ID# 1189A_50; thin section 38]). C. Narrow quartz-pyrite vein with a patchily developed poikiloblastic quartz alteration halo. The poikiloblastic quartz is optically continuous with quartz grains in adjacent segments of the vein (in cross-polarized light; width of view = 1.4 mm [Photomicrograph ID# 1189A_52; thin section 38]). D. Hairline quartz vein with relatively coarse euhedral pyrite (bluish cream color). Poikiloblastic quartz alteration is developed in the groundmass of the rock in this field of view (in simultaneous plane-polarized transmitted and reflected light; width of view = 1.4 mm [Photomicrograph ID# 1189A_54; thin section 38]).