News: Unveiling the core: X-Ray-CT images reveal FeMn nodule structure

Mariana Benites - Graduate student in geological oceanography (University of Sao Paulo) - reports on her latest research.

Ferromanganese nodules are far from being homogenous, spheroidal bodies. Different kinds of textures, porosities, nuclei, laminations, and fractures are generally present. Three-dimensional X-ray microscopy allows for the visualization of the interior structure of ferromanganese nodules by revealing contrast between light and heavy materials. White to light grey colour corresponds to heavier components, while darker grey corresponds to lighter components. The result is quite similar to a tomography of the human body, without the need of cutting or breaking it in order to discover what is going on inside.

The structure of the specimens, imaged by a Versa XRM-510 Xradia from Zeiss at the Laboratory of technological characterization, School of Engineering, University of Sao Paulo (Brazil), is clearly inhomogeneous and does not correspond to the classic model of nodules with perfectly concentric layers around a nucleus. Two main distinct growth patterns are identified, an internal and an external one, which differ mainly in layer morphology and growth direction. The internal structure is predominantly columnar, while the external portion is microlaminated.

Compositional variation between the layers is revealed by the colour alternation, even though X-ray microscopy gives no information about the chemical composition of single layers. Meanwhile, these are preliminary characterizations on which further geochemical studies will rely on in order to tell the story of how these curious rocks were formed.