Microlaminations in Marine Manganese Nodules as Revealed by Scanning Electron Microscopy
Examination of ferromanganese nodules and micronodules from the Pacific and Indian Oceans by scanning electron microscopy has revealed previously undescribed microlaminations ranging in size from less than 0.25 µm to greater than 10 µm, which appear to be the smallest structural units in manganese nodules resolvable with the SEM. These microlaminations are believed to be primary structures, as they are laterally continuous around the nodule and remain uniform in thickness in both straight and cuspate growth regions. Theories for the origin of microlaminations include short-term changes or discontinuities in nodule growth rate (possibly produced by fluctuations in bottom currents) and recrystallization or ordering phenomena associated with different mineral phases (oxidation states) of manganese/iron hydroxides.