Basaltic rocks from Holes 917A and 918D were described at a piece-by-piece scale over the following intervals: Hole 917A (Cores 152-917A-6R-1 to 152-917A-102R-3 [41.7-826.9 mbsf]); and Hole 918D (Cores 152-918D-93R-3 to 152-918D-113R-2 [1167-1310.1 mbsf]). Descriptions are based solely on hand-specimen observations, and specific clay, zeolite, and carbonate minerals are not generally distinguished, except where crystal morphology allows unequivocal identification (e.g., analcime). Readers are directed to the mineralogical work on the Hole 917A secondary minerals by Demant et al. (1998) for more detailed information.

Alteration and vein visual core description logs were used to provide a consistent and complete characterization of the core. The alteration log (Table 1) was used to describe the mineralogy and degree of alteration of each primary phenocryst phase and of the igneous groundmass. Characterization of vesicles and related alteration halos included their size, an estimate of the abundance of vesicles and halos, the mineralogy and relative timing of vug-filling minerals and mineral phases defining alteration halos, and an estimation of the proportion of filled vs. open vesicles. Visual estimates of the volume percentage of various colored groundmass alteration (e.g., oxidation halos) were recorded for each piece of the core. The vein log (Table 2) was used to record the location, orientation, mineral filling, and thickness of every vein observed in the basalts. Documentation included the presence, color, mineralogy, and thickness of associated vein halos, where present. Crosscutting relationships and the relative order of vein fillings were recorded for each feature. Table 3 provides a list of abbreviations used in these databases.

The alteration and vein data for Hole 917A are presented in Table 1 and Table 2, respectively (see "ASCII Tables" in the Table of Contents). The alteration and vein data for Hole 918D are presented in Table 4 and Table 5 (see "ASCII Tables" in the Table of Contents). The alteration and vein data are presented for Hole 917A in Figure 2 and Hole 918D in Figure 3. These diagrams provide semi-quantitative summaries of the mode of occurrence and abundance of secondary minerals from these two Holes.