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Original photo from Bundesanstalt für Geowissenschaffen und Rohstoffe (BGR)
Uploaded on Tuesday 11 Mar 2014
Physical characteristics of manganese nodules
Manganese nodules come in many shapes and sizes. They can be round, oblong, composite, or flat. Their shape can be influenced by the shape of the nucleus, the water content of the surrounding sediment, growth rates, and how often they are turned by infauna or moved by epifauna. As a general rule, smaller nodules tend to be more symmetrical. As nodules grow, they are less easily moved about by currents and animals, which leads to asymmetric growth resulting from faster diagenetic growth on the bottom and slower hydrogenetic
growth on the top.
The surface texture of nodules depends partly on the dominant mechanism of formation. Other factors that influence texture include the size of the nodules, the strength of bottom currents, sediment on the surface of the nodules, and how often the nodules are turned (Figure 7). Diagenetic nodules
tend to be rougher. Hydrogenetic nodules, in their most pure form, have a botryoidal surface (shaped like a bunch of grapes) that can be smooth or rough, but usually falls somewhere between those two extremes. If the surface is very smooth, it was likely worn down by bottom currents (Hein et al. 2000; Hayes et al. 1985).