Decorated vesicles in deep-sea basalt glass, eastern Pacific

Microprobe and scanning electron microscope (SEM) examination of small vesicles found in glassy selvages of tholeiitic basalt shows that some vesicle walls are decorated with evenly spaced spherules 0.5–4 μm across. Some are iron sulfides with high concentrations of Cu and Ni and are set in hemispherical pits in vesicle walls. Other spherules are not sulfides and appear to be aggregates of plates in microvesicular vesicle walls; these may be oxidized spherules accompanied by palagonitized glass. Other decorations include plates, grooves, and whiskers; the chemical nature of these features is not known. The spherical shape of sulfide spherules is distorted by secondary crystal growth into the vesicle, presumably due to reequilibration during cooling or to alteration. Loss of sulfide spherules during degassing may be an additional mechanism by which metals enter seawater near a rise crest.