Figure F15. Photomicrograph from the core of a black patch in Unit 15. Former medium-grained acicular crystals are replaced by trails of clear anhedral grains (feldspar and/or quartz) with lines of fine opaque grains (magnetite, hematite, and pyrite) marking the original cores of the crystals. The groundmass is mostly chlorite (Sample 193-1189A-8R-1 [Piece 17, 103-105 cm]; width of view = 2.75 mm. Photomicrograph ID# 1189A

Figure F15. Photomicrograph from the core of a black patch in Unit 15. Former medium-grained acicular crystals are replaced by trails of clear anhedral grains (feldspar and/or quartz) with lines of fine opaque grains (magnetite, hematite, and pyrite) marking the original cores of the crystals. The groundmass is mostly chlorite (Sample 193-1189A-8R-1 [Piece 17, 103-105 cm]; width of view = 2.75 mm. Photomicrograph ID# 1189A_99; thin section 54).