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Figure F18. Photomicrographs of a chilled margin of sparsely phyric nonvesicular basalt, Unit 1 (Sample 336-U1383C-2R-2, 15–18 cm [Piece 3], Thin Section 28). A. Whole thin section photomicrograph showing three domains across the chilled margin. From right to left: (1) fresh glass with euhedral plagioclase and olivine crystals surrounded by spherulitic rim, resulting in glass devitrification; (2) bright yellowish-brown palagonite with higher intensity of spherulitic texture; and (3) cryptocrystalline mesostasis formed by coalescent spherulites. Field of view (FOV) = 5 mm; single-polarized light. B. Photomicrograph of area in A, showing contact between spherulite, palagonite, and fresh glass. Microtubules extending from alteration patches into fresh glass are common. FOV = 0.5 mm; single-polarized light. C. Photomicrograph of palagonite/fresh glass interface with sharp contact, gradual alteration bands, and absence of microtubules. FOV = 0.25 mm; single-polarized light.

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