**3. Conclusion**

A comprehensive layer-by-layer analysis of the ferromanganese crust showed that the crust is practically a composite consisting of clastic and volcanogenic micron-sized minerals and stromatolites, consisting of fossilized biofilms filled with nanoparticles of iron and manganese oxide compounds, which are bacteria waste products. The lower layers of the crust are very dense: they contain many clastic minerals, and ore-bearing stromatolites grow between them. During the growth of the crust, bacteria constantly carry out their vital activity, therefore stromatolites grow continuously, occasionally changing their direction and shape under the influence of external conditions. And minerals: apatite, quartz and others come to the place of crust growth only occasionally - after a volcanic eruption. Therefore, the proportion of the iron-ore and manganese-ore components increases from the lower crust layer to the upper layer, which is almost entirely composed of these components. This leads to the fragility of the upper layers of the crust.

Experimental methods have provided objective evidence of the biogenic nature of the ore components of ferromanganese crusts. And the method of Mössbauer spectroscopy, first applied to these objects, made it possible to obtain a quantitative phase analysis of iron ore components in different layers of the crust. Based on this analysis, it was possible to trace how the composition of iron oxides changes in different layers of the crust, depending on changes in external conditions.

*Iron Ores*
