INVESTIGADORES
STEWART Silvana Jacqueline
congresos y reuniones científicas
Título:
DRUSE PYROXENES IN D´ORBIGNY: A MÖSSBAUER SPECTROSCOPY STUDY
Autor/es:
R.B. SCORZELLI, I. SOUZA ACEVEDO, S. J. STEWART, M. E. VARELA, G. CURAT,
Lugar:
USA
Reunión:
Congreso; 67th Meteoritical Society Meeting; 2004
Resumen:
DOrbigny is the sixth and by far the
largest angrite known. It is peculiar with respect to three
features: the abundance of hollow shells, the abundant presence of glasses and
the presence of abundant open druses with perfectly crystallized augites of prismatic
habit [2-3]. Here we report on the distribution of Fe2+
among the non-equivalent sites in the druse pyroxenes of the DOrbigny
meteorite as determined by Mössbauer spectroscopy.
Sample: Our specimens consisted of 200
mg of euhedral augites, ranging in size from 70 to 400 mm . Electron microprobe
analyses showed that augites are chemically homogeneous with a slight compositional
change at the outermost ~ 5 µm (rim): SiO2 - 46.4 (45) wt%, TiO2
- 1.53 (1.91) wt%, Al2O3 - 8.1 (9.4) wt%, FeO - 12.7 (13)
wt%, MgO - 9.1 (8.3) wt%, CaO - 22.7 (22.9) wt%.
Results and Discussion: The study of cation
distributions over non-equivalent lattice sites in minerals can provide
valuable information on its pT history. In pyroxene crystals that have been
cooled slowly to temperatures lower that 500 ºC, the Fe2+ ions
populate primarily the M2 position whereas the Mg2+ ions
occupy predominantly the M1 position. In crystals that have been
rapidly cooled, a more disordered Mg, Fe distribution over the M1
sites is observed.
The Mössbauer spectra of DOrbigny druse Augites
obtained at room temperature consist of an intense inner doublet due to Fe2+
at the M2 sites and a less intense outer doublet due to Fe2+
at the M1 sites. Most Fe is present as Fe2+ but traces of
Fe3+ have also been observed