Ferruginous vernadite in an Indian Ocean ferromanganese nodule

Select area electron diffraction and microanalysis of the optically dark component of a ferromanganese nodule from the South East Indian Ocean Manganese Field indicate that this is composed of a random stratification of crystallites of vernadite MnO 2 . (R 2 O, RO, R 2 O 3 ) x . y H 2 O, where R represents elements such as K, Ba, Na, Ca, Mg, and a disordered hydrated iron oxide, possibly ferrihydrite 5Fe 2 , O 3 . 9H 2 O or feroxyhyte δ′-FeOOH. Whether the dark component is an irregular mixed-layer hybrid mineral or a layered accumulation resulting from epitaxy of the above phases is uncertain.