QUANTITATIVE IR SPECTROSCOPIC DETERMINATION OF THE COMPONENT H2O IN STAUROLITE

Staurolite exhibits a complex IR absorption band system in the range o f 3750 to 3250 cm-l due to OH stretching vibrations. The bands show a strong pleochroism with nearly no absorbance in spectra with E // b an d strong (intermediate) absorbance in spectra with E // a (E // c). Th e total integrated absorbance was determined from spectra of (010) sta urolite plates. These spectra were polarized with E ii a and E ii c. T he total integrated molar absorption coefficient (epsilon(i,tot) = 830 00 +/- 5000 l.mol(H2O)(-1).cm(-2)) was calculated using H2O contents a s determined from independent physico-chemical measurements (''Kari-Fi scher'' titration). Based on Lambert-Beer's law, the content of the co mponent H2O in staurolite is obtained with a relative standard deviati on of 9 % (1 sigma) using this epsilon(i,tot) value and by measuring t he total integrated absorbance of the whole band system from polarized spectra of a (010) staurolite plate. The quantitative IR data on stau rolite are in good agreement with the IR absorption calibrations for w ater in minerals by Paterson (1982) and Libowitzky & Rossman (1997).