Crystal chemistry and infrared spectroscopy in the OH-stretching region of synthetic staurolites
Authors: M. Koch-Müller, K. Langer, G. Schuck and H. BehrensJournal-ref: Eur. J. Mineral., 9 (1997) 67-82 , PDF
Abstract: Fe-staurolite synthesized in
the pressure range 5 to 25 kbar at 680 °C was analysed by microprobe and
by a titration method (for water-contents) which uses the
“Karl-Fischer” reaction and also characterized by FT-infrared powder
spectroscopy in the OH-stretching region (3000-4000 cm-1). The study
shows that the stoichiometry of the synthetic Fe-staurolites depends on
the pressure of equilibration, with Fe pfu decreasing with increasing
pressure, according to the heterovalent substitution of Fe2+ by Al3+ in
the T2 site. This chargeincreasing substitution is combined with
charge-reducing substitutions in the “kyanite’Mayer and by vacancies in
the proton site HI. The incorporation of Al in T2 is supported by
peculiarities of the IR-spectra in the range of the OH-valence
vibrations.
Mg- and Zn-staurolite were synthesized at 25 kbar and 700 °C and
investigated by infrared spectroscopy. The comparison of the infrared
spectra of synthetic Fe-, Mg- and Zn-staurolites shows that there is a
significant amount of Fe2+, Mg and Zn in the respective M2 sites.
Key-words: synthetic staurolites, staurolite stoichiometry, Karl-Fischer
titration, infrared spectroscopy, OH-stretching region.