The structure and crystal chemistry of vernadite in ferromanganese crusts

Abstract

The structure and crystal chemistry of vernadite in ferromanganese crusts from the Magellan Seamount in the north-west Pacific Ocean have been investigated using synchrotron X-ray diffraction (XRD), X-ray pair distribution function (PDF) and high-resolution transmission electron microscopy (TEM). XRD patterns of vernadite mainly show two strong diffraction peaks at 2.42-2.43 Å and 1.41 Å without or with a broad (001) diffraction peak, indicating thin layer nanophases along the c-direction. TEM images show flat and curved sheet-like nanocrystals with (001) layer thickness of $7.2 Å and $9.6 Å , and their interstratified structure. PDF patterns of the vernadite are similar to those from synthetic -MnO 2 and defective birnessite, suggesting a phyllomanganate framework. Combined XRD/PDF patterns suggest that vernadite in the outer part is associated with a higher density interlayer species at triple-edge sharing sites. The proportion of the 10 Å phase increases from the outer (young) part to the inner (old) part of the Mn crusts due to aging and sorption of Mn, Co and Ni from ambient seawater. This study suggests that this combined method of synchrotron radiation XRD/PDF and high-resolution TEM is a powerful tool to determine atomic structures of poorly crystallized nano-minerals. The mixture model of vernadite structure will help to understand the partitioning and distribution of trace elements in the ferromanganese crusts.

Raman spectroscopy study of manganese oxides: Layer structures

“…Vernadite is found in the oxidized zone of Mn-rich deposits and might be a major phase in ocean Mn nodules and crusts (Chukrov et al 1987). Vernadite often is assumed to be analogous to the synthetic phase δ-MnO 2 (Villalobos et al 2003;Grangeon, 2010;Lee et al 2019), although the term δ-MnO 2 has been applied very broadly in recent years. Some have suggested that its formation is primarily mediated by biota (Chukrov et al 1987;Grangeon et al 2012).…”

“…Webb, 2005). Others use pair distribution function modeling to assess the symmetry and other structural details (Yang et al 2019;Lee et al 2019). A drawback of both approaches is that data must be collected using synchrotron sources.…”

“…In addition, different synthesis methods and treatments have been employed to produce "δ-MnO 2 " phases, which are not always identical. Lee et al (2019) concluded from their TEM and PDF studies of ocean crust vernadite that this phase is best modeled by interstratified structures with 7 and 10 Å interlayer spacings. Our preliminary results suggest that Raman spectroscopy is a useful tool for characterizing and comparing similarities and differences among natural vernadites and synthetic δ-MnO 2 phases.…”

Genesis and Evolution of Ferromanganese Crusts from the Summit of Rio Grande Rise, Southwest Atlantic Ocean

“…Two types of Mn oxides were observed in the Fe-Mn crusts of RGR. The first has no basal reflection and diagnostic reflections at 2.45 Å and 1.42 Å, which correspond to the disordered phyllomanganate vernadite [36,37], also termed Fe-vernadite by some authors because it corresponds to Vernadite epitaxially intergrown with amorphous FeOOH [35,38,39]. The second has basal reflections at 10 Å and 5 Å and possible reflections overlapping with those of Vernadite at 2.45 Å and 1.42 Å peaks, which are together characteristic of 10 Å phyllomanganates, which can be either disordered 10 Å vernadite, or ordered buserite or asbolane, or a mixture of them [35,[40][41][42][43].…”

Polymorph exploration of bismuth stannate using first-principles phonon mode mapping

“…To investigate this, we performed Rietveld analysis of a series of powder diffraction patterns collected from 300-1100 K in which the isotropic atomic displacement parameters (ADPs) of the inequivalent Bi sites were independently rened (4 in a, 5 in b, 1 in g). The ADPs can provide valuable structural information, [31][32][33] and while this analysis pushes the information content of powder diffraction to its limits, we nd that the Bi4 and Bi5 atoms, which disorder during the phase transition, have ADPs in the b phase comparable to those in g-Bi 2 Sn 2 O 7 and much larger than the other Bi atoms (Fig. S12 †).…”