Figure F41. Photomicrographs of altered olivine (Ol). We see similar clay pseudomorphs after olivine throughout the basalt units, especially in the margins of flows. A. Typical chilled margin (Sample 183-1137A-25R-3, 90-93 cm, base of Unit 1). B. Least-altered chilled margin (Sample 183-1137A-29R-2, 71-74 cm, top of Unit 4). Both images are in plane-polarized light; field of view width = 1.4 mm.