We examined formation of roentgenoamorphous nano-dimensional manganous oxide from positions of biogenic mineral formation. Objects of our researches were nanodimensional phases of the oceanic ferromanganous nodules. Electronic-microscopic investigations showed a great expansion of mineralized biofilms on the studied samples. The content of the bacterial mass makes (%): MnO - 28.34; Fe203 - 17.14; Si02 - 7.11; CaO - 2.41; Ti02 - 1.90; NazO- 1.74; A1203 - 1.73; MgO - 1.30; P205- 1.25; S03- 1.25; CoO - 0.68; CuO - 0.54; NiO - 0.53; K20 - 0.50. The use of atomic-force microscopy method allows determining size of some cells of cyanobacteria with the 200nm at length and about 70 nm across diameter. Inclusions of native metals (copper, iron, zinc) with the size from 10 to 20 μn were found in the ore areas of ferromanganese nodules. Formation of the native metals can be explained by an accumulation of organic matter as a result of formation of microscopic areas with abrupt recovery conditions.