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Degeneration of biogenic superparamagnetic magnetite
Author(s) -
LI Y.L.,
PFIFFNER S. M.,
DYAR M. D.,
VALI H.,
KONHAUSER K.,
COLE D.R.,
RONDI A. J.,
PHELPS T. J.
Publication year - 2009
Publication title -
geobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.859
H-Index - 72
eISSN - 1472-4669
pISSN - 1472-4677
DOI - 10.1111/j.1472-4669.2008.00186.x
Subject(s) - magnetite , superparamagnetism , mössbauer spectroscopy , chemistry , materials science , mineralogy , chemical engineering , crystallography , metallurgy , magnetization , magnetic field , physics , quantum mechanics , engineering
Magnetite crystals precipitated as a consequence of Fe(III) reduction by Shewanella algae BrY after 265 h incubation and 5‐year anaerobic storage were investigated with transmission electron microscopy, Mössbauer spectroscopy and X‐ray diffraction. The magnetite crystals were typically superparamagnetic with an approximate size of 13 nm. The lattice constants of the 265 h and 5‐year crystals are 8.4164Å and 8.3774Å, respectively. The Mössbauer spectra indicated that the 265 h magnetite had excess Fe(II) in its crystal‐chemistry (Fe 3+ 1.990 Fe 2+ 1.015 O 4 ) but the 5‐year magnetite was Fe(II)‐deficient in stoichiometry (Fe 3+ 2.388 Fe 2+ 0.419 O 4 ). Such crystal‐chemical changes may be indicative of the degeneration of superparamagnetic magnetite through the aqueous oxidization of Fe(II) anaerobically, and the concomitant oxidation of the organic phases (fatty acid methyl esters) that were present during the initial formation of the magnetite. The observation of a corona structure on the aged magnetite corroborates the anaerobic oxidation of Fe(II) on the outer layers of magnetite crystals. These results suggest that there may be a possible link between the enzymatic activity of the bacteria and the stability of Fe(II)‐excess magnetite, which may help explain why stable nano‐magnetite grains are seldom preserved in natural environments.