INVESTIGADORES
VARELA Maria Eugenia
artículos
Título:
Druse clinopyroxene in D?Orbigny angritic meteorite studied by single-crystal
Autor/es:
ABDU, Y.; SCORZELLI R,; VARELA, M.E; KURAT G,; SOUZA AZEVEDO, I.; STEWART S,; HAWTHORNE F.
Revista:
METEORITICS & PLANETARY SCIENCE
Editorial:
METEORITICAL SOC
Referencias:
Año: 2009 vol. 44 p. 581 - 587
ISSN:
1086-9379
Resumen:
The crystal structure of druse clinopyroxene from the D?Orbigny angrite, (Ca0.944 Fe2+ 0.042 Mg0.010Mn0.004) (Mg0.469Fe2+ 0.317Fe3+0.035Al0.125Cr0.010Ti0.044) (Si1.742Al0.258) O6, a = 9.7684(2), b = 8.9124(2), c = 5.2859(1) Å, β = 105.903(1)°, V = 442.58 Å3, space group C2/c, Z = 2, has been refined to an R1 index of 1.92% using single-crystal X-ray diffraction data. The unit formula, calculated from electron microprobe analysis, and the refined site scattering values were used to assign site populations. The distribution of Fe2+ and Mg over the M1 and M2 sites suggests a closure temperature of 1000 °C. Mössbauer spectroscopy measurements were done at room temperature on a singlecrystal and a powdered sample. The spectra are adequately fit by a Voigt-based quadrupole-splitting distribution model having two generalized sites, one for Fe2+ with two Gaussian components and one for Fe3+ with one Gaussian component. The two ferrous components are assigned to Fe2+ at the M1 site, and arise from two different next-nearest-neighbor configurations of Ca and Fe cations at the M2 site: (3Ca,0Fe) and (2Ca,1Fe). The Fe3+/Fetot ratio determined by Mössbauer spectroscopy is inagreement with that calculated from the electron microprobe analysis. The results are discussed in connection with the redox and thermal history of D?Orbigny.