Birnessite/todorokite, uncharacterized iron and manganese hydroxides. Pacific Ocean
A manganese nodule in which a radiolarian test (centre) lies within collomorphic banding of iron- and manganese-bearing hydroxides. Higher reflectance bands are mixtures of birnessite and todorokite, whereas lower reflectance bands are browner and less well polished and comprise uncharacterized iron and manganese hydroxides and oxides. Black areas are polishing pits. It is not possible to identify individual minerals within manganese nodules by reflected light microscopy alone.
Polished block, plane polarized light, x 80, air