Ten nodules from 7 different ore fields from Kara sea were studied. Each sample has been allocated several zones (2 to 4), which have been studied by X-ray diffraction, electron microprobe analysis, optical and electron microscopy. XRD showed manganese minerals (birnessite and / or boozerite-1) in all studied samples. Clay matter is composed of chlorite, montmorillonite, kaolinite and mica. Iron-phase as a mineral (goethite) detected in 1 sample. In other cases, iron-bearing interlayers stacked X-ray amorphous material. Microprobe analysis confirmed the presence of at least two different manganese minerals, which differ in morphology and chemical composition. Iron and manganese interlayers alternated and have distinct spatial boundaries.
Keywords: ferromanganese nodules, birnessite, boozerite, goethite