Abstract:SUMMARYIndex terms: magnetization, Mössbauer, magnetic soil.
RESUMO: VARIABILIDADES COMPOSICIONAL E ESTRUTURAL DE ÓXIDOS DE FERRO RICOS EM Mg DE TUFITO
“…Grãos magnéticos desse tufito e de frações grosseiras do solo derivado tendem a preservar porções variáveis de magnetita (Fabris et al, 1995;Ferreira et al, 1997;Fabris et al, 1997a, b;Mussel et al, 1999).…”
“…Grãos magnéticos desse tufito e de frações grosseiras do solo derivado tendem a preservar porções variáveis de magnetita (Fabris et al, 1995;Ferreira et al, 1997;Fabris et al, 1997a, b;Mussel et al, 1999).…”
SUMMARYThe main objective of this work was to characterize the magnetic minerals and to identify their pedogenic transformation on a steatite-forming soil of Minas Gerais, Brazil. The iron-rich spinel phase was characterized by chemical analysis, powder X-ray diffraction, Mössbauer spectroscopy, with and without an externally applied magnetic field of 6 tesla, and saturation magnetization measurements. Nearly stoichiometric and well-crystallized magnetite was the only magnetic mineral actually detected. The cubic unit cell parameter of the fresh rock magnetite was found to be a o = 0.8407(5) nm. Hematite (hexagonal cell; a = 0.5036(3) nm, c = 1.375(4) nm) was detected in the altered rock and in the sand-soil and silt-soil fractions. Magnetite is assumed to transform into hematite during pedogenesis through progressive oxidation of structural Fe 2+ to Fe 3+ . In partially oxidized magnetites, a relatively small proportion of Fe 3+ was interpreted as being uncoupled from the Fe 2+ -Fe 3+ charge transfer system, in octahedral sites of the spinel structure. Compositional formulae of magnetite with different degrees of non-stoichiometry are proposed. Ilmenite was found in minor proportions in the magnetically extracted portions from both rock and soil samples.Index terms: Iron-rich spinel, iron oxide, soapstone, magnetic soil, Mössbauer spectroscopy.(1) This work is part of the thesis of the first author, presented to the Departmento
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