Secondary minerals and geochemistry in basalts at DSDP Leg 67 Legs

Secondary minerals in basalts from Holes 495 and 500 include smectite and chlorite, both of which have partially replaced the basalt groundmass. In addition to these two minerals, amphibole, laumontite, albite, and a corrensitelike mineral are present in Holes 499B and 499C. Smectite, chlorite, talc, calcite, phillipsite, mica, and mixed-layer chlorite-montmorillonite also fill veins in the basalts of Hole 495. The secondary mineral assemblages from Site 499 are characteristic of the initial stage of greenschist facies metamorphism

Chemical composition of Fe-Mn nodules from the Pacific Ocean

Calcareous and siliceous biogenic components have been studied in deep-water iron-manganese nodules from the northern and southern Pacific Ocean. Calcareous material consists of foraminifera remains, calcareous algae, and coccolithophorids, whereas siliceous material consists of remains of radiolarians and diatoms, as well as sponge spicules. Structures similar in morphology to coccal and filiform bacteria have been found in both outer and inner sections of the nodules indicating that microorganisms may be directly or indirectly involved in their development

Age and chemical composition of altered basalts

Study of morphology of clay minerals formed in altered submarine basalt flow lava has shown that clay-forming process was a continuous-discontinuous one. Basaltic glass was the most readily replaced and laminar-packet aggregates of smectite were produced. Acicular-globular smectites were also formed from solutions in cavities within basalts

Geochemistry, SiO2 minerals and isotopes at DSDP Hole 72-516F

Cherts recovered during DSDP Leg 72 from Rio Grande Rise sediments (Site 516) consist of both cristobalite and quartz, and contain ghosts of foraminifers and (more rare) radiolarians. Porcelanite made of disordered cristobalite is found in most old enclosing sediments. Local dissolution of siliceous microfossils during diagenesis is the most likely source of the silica required for the chert formation. As sediment age increases, the proportion of biogenic silica decreases and authigenic silica increases