Slightly altered basalt was recovered throughout Hole 1153A. The degree of alteration differs from piece to piece and is more intense along margins and around fractures and vesicles. Approximately 70% of the vesicles are coated or filled by any or all of the following: cryptocrystalline silica, Fe oxyhydroxide, calcite, and rare zeolites (Section 187-1153A-8R-2 [Pieces 3 and 6]). The same alteration products are found as fracture fillings, again with the addition of carbonate material. Large (up to 0.8 cm) calcite-filled cavities occur in the lower half of Section 187-1153A-8R-2 (Fig. F3) and make up 2% of the rock. A single angular basalt fragment (Section 187-1153A-8R-1 [Piece 11]) is entirely covered by a 0.5-mm-thick layer of calcite (Fig. F4). Attached to this piece is a 2- to 3-cm-long strongly altered chilled (pillow?) margin in which small amounts of fresh glass are still preserved. Brown Fe oxyhydroxide entirely covers some fractures (e.g., Section 187-1153A-8R-1 [Piece 16B]) and extends for up to 10 mm around some fractures and up to 25 mm from the edges of pieces not cut by the drill (e.g., Section 187-1153A-8R-2 [Piece 2]). Fe oxyhydroxide frequently highlights igneous textures (e.g., the spherulitic plagioclase in Figs. F5 and F1). Small (1-2 mm) spots of Mn oxide are visible on fractured surfaces. In thin section, some groundmass olivine appears iddingsitized, whereas groundmass plagioclase is unaffected by alteration. A general overall decrease of Fe oxyhydroxide and smectite abundance toward the center of basalt fragments confirms the macroscopic observations, that the interior of the basalt fragments are least altered. Interstitial glass has been replaced by an opaque orange-brown material. Palagonite has replaced a large portion of most glassy rinds (e.g., Fig. F6). The degree of palagonitization is highest (~90%) on the outer layers of glass rinds (e.g., Section 187-1153A-8R-1 [Piece 5]) or in Section 187-1153A-8R-1 (Piece 14) at the center of a glass rind believed to mark the contact between two pillows. Palagonitization drops to <25% within a few millimeters and thereafter predominantly occurs along cracks. The centers of palagonite-filled cracks in Section 187-1153A-8R-1 (Piece 4) are occupied by silica veins, which are thickest (up to 1 mm) at the outer, most altered edges of the glass rind. The palagonite is symmetrically arranged around the silica, suggesting that the silica precipitated along an expanding crack after significant palagonitization had occurred. In Section 187-1153A-8R-1 (Piece 14), two thick (3 mm) calcite veins crosscut the center of a pillow rind (Fig. F7) and no silica can be observed under the binocular microscope, suggesting that different fluids have percolated through the lava pile. The most likely source for the calcite-bearing fluids is the carbonate overlying the basalt at Site 1153, whereas the cryptocrystalline silica may be derived from the hydrated glass. Whether these reflect temporal or local variations, however, is unknown.