POLARIZED SINGLE-CRYSTAL FTIR-SPECTRA OF NATURAL STAUROLITE

Polarized infrared absorption spectra of thin single-crystal slabs par allel to (010) and (001) of a staurolite from Pizzo Forno, Ticino, wit h analyzed composition (Fe2.9Mg0.9Zn0.1Mn0.1)Al17.5Ti0.1(Si7.7Al0.3)O4 8H3 have been measured in the range of 3000-4000 cm(-1) the pleochroit ic behaviour of the OH-vibrations three groups of bands can be disting uished: the bands of group I, a strong band at 3445 cm(-1) plus a weak shoulder at 3358 cm(-1), and the bands of group II, a weak band cente red at 3677 cm(-1) plus a shoulder at 3635 cm(-1), are assigned to the H1 and H2 protons, respectively. The bands of group III, a weak band at 3577 cm(-1) plus a shoulder, cannot be interpreted on the basis of the proton positions known so far. We assign them to an additional pro ton H3, which is bonded to O1 and shows a bifurcated hydrogen bridge t o two O5 in a vacant T2 site.