The igneous units are intercalated with chert-rich sediments, which are often baked at the contact with the basalt. The alteration intensity is highly variable in these rocks, and their colors vary from gray black to green gray and to light brown. The MgO-rich lavas contain abundant olivine phenocrysts, which are only rarely observed deeper in the section. The most evolved lavas, those with the lowest MgO and highest Zr, are commonly triple saturated in olivine, plagioclase, and clinopyroxene. In general, phenocrysts are scarce in the entire section drilled during Leg 185.
Plagioclase is the most common phase, but most of the lavas are classified as aphyric.
A second Si-rich hydrothermal unit is present deeper in the section at 630 mbsf. This unit marks a change in magma composition and, thus, probably represents a significant hiatus in the volcanic evolution. The amount of interpillow material of probable sedimentary origin decreases significantly downsection in this sequence. The thickest flow in the former exceeds 20 m. The logging data along with the FMS images will be integrated with the core descriptions to create as complete a section as possible from which the bulk geochemical composition of the upper oceanic crust at this site will be calculated.