Basalt was recovered from Hole 1154A between 233.2 and 265.8 mbsf. Total recovery was 9.42 m, equal to 27.38%. All recovered basalt was assigned to a single unit of light gray, moderately plagioclase-olivine phyric pillow basalt (Fig. F1). The basalt has undergone <10% low-temperature alteration (see "Alteration"). Of 198 recovered pieces, 26 (~13%) include glassy pillow rinds and/or chilled margins. The glass zone of chilled margins ranges from 8 to <1 mm in width but is 2-3 mm in most cases. Glass ranges from fresh to strongly altered (see "Alteration"). Small (<1 mm), euhedral to subhedral olivine and plagioclase phenocrysts are present in some of the thicker glass rinds (e.g., Section 187-1154-6R-1 [Piece 2]).
Phenocryst abundance varies throughout the core from 2% to 5% with an average of ~3%. Prismatic to tabular, subhedral plagioclase phenocrysts are from 0.5 to 6 mm in length and make up 2%-3% of the rock. In thin section, partially resorbed cores, twinning, and zoning are visible in some crystals (Figs. F2, F3). In addition, some plagioclase crystals display quench crystallization overgrowths (Fig. F2). A large (3-4 mm) anhedral plagioclase xenocryst, presumably rounded during magma transport, was identified in thin section (Sample 187-1154A-7R-1, 140-145 cm). Most plagioclase phenocrysts are fresh, but some are altered to clay and Fe oxyhydroxide within 0.5- to 2-cm-wide alteration halos that parallel fractures and exterior surfaces. Equant, euhedral to subhedral olivine is the second most abundant phenocryst phase (0.5%-1%) and ranges from 0.5 to 3 mm. Rare, skeletal olivine microphenocrysts are also present (Fig. F4). Within the alteration halos, most of the olivine is replaced (90%-100%) by Fe oxyhydroxide. In the fresher centers of individual basalt pieces, olivine appears fresh but is, in places, coated by a white clay mineral and/or flakes of cryptocrystalline silica (see "Alteration"). In thin section, replacement by Fe oxyhydroxide and clay is visible along grain boundaries of some olivines. Glomerocrysts of plagioclase and plagioclase plus olivine make up 10%-15% of the phenocryst assemblage. The source of the unsystematic variation in phenocryst modal proportion cannot be precisely determined from the level of shipboard observation.
Chilled pillow margins exhibit a variety of quench crystallization textures, ranging from spherulitic to plagioclase sheaf to clinopyroxene plumose forms. Figure F5 shows typical plagioclase spherulites surrounded by clear glass, partially replaced by smectite. Acicular plagioclase forms the cores of the spherulites. The proportions of the groundmass phases cannot be accurately quantified because of the predominance of cryptocrystalline quench textures over most of the chilled margin. The groundmass of pillow interiors typically has an intersertal texture, with prismatic to lath-shaped plagioclase in roughly equal proportion to granular clinopyroxene, minor equant olivine, and interstitial glass (Fig. F6). Spherical vesicles, <1 mm in diameter, make up 1% of the rock.