Electron paramagnetic resonance of phytofulgurite

Doklady Earth Sciences -     

Local heterogeneity in the distribution of iron ions in CR-spinel from Ural ultramafic massifs: Evidence from Mössbauer spectroscopy data

The crystal chemistry of Fe ions in Cr-spinel from the largest Ural ultramafic massifs has been studied by Mössbauer spectroscopy at room temperature and the boiling temperature of liquid nitrogen. The spectra substantially depend on the mineral composition (stoichiometry) and measurement temperature; Fe²⁺ and Fe³⁺ doublets significantly overlap; the Fe²⁺ doublet lines are markedly broadened. According to the Mössbauer data, the degree of iron oxidation is 7–35% and appreciably differs from that in the stoichiometric approximation. The disturbance of integral stoichiometry by di- and trivalent cations (deviation of the Me³⁺/Me²⁺ value from 2.0) may be caused not only by partial inversion of the mineral structure but also by local micro- and nanoscale heterogeneity of the mineral, clustering of Fe²⁺ and Al (Cr, Fe³⁺) cations, and the appearance of associates. Possible application of the QS-distribution method for analyzing nonequivalent nuclear iron states and the thermal dynamics of Mössbauer spectra for studying local clustering effects of iron cations is discussed. It is shown that these approaches give new information on local heterogeneity of structural sites occupied by iron ions.     

Biomineral nanostructures of manganese oxides in oceanic ferromanganese nodules

Manganese oxides, which are widespread and of great practical importance, are formed and transformed by the active role of microorganisms. Manganese aggregates occur as both crystallized varieties and disordered fine-grained phases with significant ore grade and up to 50–60 vol % of X-ray amorphous components. X-ray amorphous nanosized Mn oxides in Fe-Mn nodules from the Pacific Ocean floor were examined from the standpoint of their biogenic origin. SEM examination showed abundant mineralized biofilms on the studied samples. The chemical composition of bacterial mass is as follows (wt %): 28.34 MnO, 17.14 Fe₂O₃, 7.11 SiO₂, 2.41 CaO, 17.90 TiO₂, 1.74 Na₂O, 1.73 Al₂O₃, 1.30 MgO, 1.25 P₂O₅, 1.25 SO₃, 0.68 CoO, 0.54 CuO, 0.53 NiO, and 0.50 K₂O. The chemical composition of fossilized cyanobacterial mats within the interlayer space of nodulesis as follows (wt %): 48.35 MnO, 6.23 Fe₂O₃, 8.76 MgO, 5.05 Al₂O₃, 4.45 SiO₂, 3.63 NiO, 2.30 Na₂O, 2.19 CuO, 1.31 CaO, and 0.68 K₂O is direct evidence for participation of bacteria in Mn oxide formation. This phase consists of mineralized glycocalix consisting of nanosized flakes of todorokite. Native metals (Cu, Fe, and Zn) as inclusions 10–20 μm in size were identified in ferromanganese nodules as well. The formation of nativemetals can be explained by their crystallization at highly reducing conditions maintained by organic matter.