Figure F16. Photomicrograph from near the edge of a black patch in Unit 15. A small amount of host rock is visible along the left edge. The clear grains in the middle outline a 2-mm-long area, possibly originally a plagioclase phenocryst, that consists of optically oriented clear material (secondary feldspar or quartz?) (Sample 193-1189A-8R-1 [Piece 17, 103-105 cm]; width of view = 2.75 mm). A. Plane-parallel illumination (Photomicrograph ID# 1189A_100; thin section 54). B. Cross-polarized illumination (Photomicrograph ID# 1189A

Figure F16. Photomicrograph from near the edge of a black patch in Unit 15. A small amount of host rock is visible along the left edge. The clear grains in the middle outline a 2-mm-long area, possibly originally a plagioclase phenocryst, that consists of optically oriented clear material (secondary feldspar or quartz?) (Sample 193-1189A-8R-1 [Piece 17, 103-105 cm]; width of view = 2.75 mm). A. Plane-parallel illumination (Photomicrograph ID# 1189A_100; thin section 54). B. Cross-polarized illumination (Photomicrograph ID# 1189A_101; thin section 54).