ICATE   21876
INSTITUTO DE CIENCIAS ASTRONOMICAS, DE LA TIERRA Y DEL ESPACIO
Unidad Ejecutora - UE
artículos
Título:
Druse clinopyroxene in D’Orbigny angritic meteorite studied by single-crystal X-ray diffraction, electron microprobe analysis and Mössbauer spectroscopy.
Autor/es:
ABDU, Y.; SCORZELLI, R; VARELA, M.E; KURAT, G; IZABEL DE SOUZA AZEVEDO; SILVANA J. STEWART; FRANK C. HAWTHORNE
Revista:
METEORITICS & PLANETARY SCIENCE
Referencias:
Año: 2008
ISSN:
1086-9379
Resumen:
Abstract The crystal structure of druse clinopyroxene from the D’Orbigny meteorite, (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) Å, b = 8.9124(2) Å, 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. 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 an equilibration temperature of 1000 ºC. Mössbauer spectroscopy measurements of D’Orbigny druse clinopyroxene have been carried out on powdered and single-crystal samples at room temperature, and on druse clinopyroxene separate in the temperature range (300 K – 70 K). The spectra are adequately fitted to a Voigt-based quadrupole splitting distribution model having two generalized sites, one for Fe2+ with two Gaussian components and one for Fe3+ with only one Gaussian component. The two ferrous components are assigned to Fe2+ in the M1 site, and arise from two different next-nearest-neighbour configurations of Ca and Fe cations in the M2 site: (3Ca,0F) and (2Ca,1Fe). The temperature dependence of the QS of Fe2+ in M1(3Ca,0F) and M1(2Ca,1Fe) is discussed in connection with the relative local distortion from octahedral coordination. The small amount of Fe2+ in the M2 site could not be resolved by Mössbauer spectroscopy. The Fe3+/Fetot ratio determined by Mössbauer spectroscopy is in agreement with that calculated from electron microprobe analysis, and may indicate the formation of D’Orbigny druse clinopyroxene under oxidizing conditions.