Figure F66. Thin section photomicrographs of altered olivine and groundmass. A. Completely altered phenocryst of olivine to green clay (outer part) and calcite (moderately olivine-phyric lava lobe) (Sample 330-U1377A-6R-2, 64–66 cm; Thin Section 275) (with crossed polars). B. Highly altered groundmass to green and brown clay and slightly altered phenocrysts of plagioclase (aphyric basalt lava body or intrusive sheet) (Sample 330-U1377A-3R-1, 68–70 cm; Thin Section 270) (with crossed polars). C. Vesicles (sparsely olivine-phyric lava lobe) filled with thin layer of brown clay at rim and later by white clay and carbonates (Sample 330-U1377A-6R-2, 13–15 cm; Thin Section 274) (with crossed polars). D. Vuggy vein (aphyric basalt lava body or intrusive sheet) filled with mix of clay minerals, Fe oxyhydroxides, and goethite (Sample 330-U1377A-3R-1, 68–70 cm; Thin Section 270) (plane-polarized, transmitted light).
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