**2. Analysis of ferromanganese crusts phase composition and morphology**

A characteristic feature of ferromanganese crusts is their layered structure, which shows a history of their origin and growth. If the crust is sliced, one can usually observe from 3 to 5 layers with an average thickness of 2–3 cm, differing in structure, physical properties and composition of components. Usually, the lower layers of the crust are dense and strong, while the upper layers are more porous and brittle. It is possible to consistently trace the processes of ore accumulation and global changes in the external conditions for the formation of ferromanganese crusts by studying the composition and structure of these layers.
