Birnessite/todorokite, uncharacterized iron and manganese hydroxides. Pacific Ocean
In this manganese nodule, collomorphic banding comprises intimate mixtures of manganese- and iron-bearing hydroxide minerals. Higher reflectance bands (white-grey) are bireflecting and anisotropic (in oil) and comprise birnessite and todorokite. Their presence was confirmed by X-ray diffraction. Lower reflectance bands (brown-grey) comprise poorly crystalline manganese and iron hydroxides and are less well polished. A detrital silicate grain (dark grey, bottom centre) is present. Medium grey areas are mainly resin and black areas are polishing pits.
Polished block, plane polarized light, x 80, air