FTIR spectroscopy in the OH-stretching region of monoclinic epidotes from Praborna (St. Marcel, Aosta Valley, Italy)

The 14 analysed epidote samples examined from Praborna range in composition from clinozoisite to Sr-rich piemontite. In the OH-stretching region, (Al,Fe (super 3+) )-clinozoisites show a single broad band centred in the range 3345-3380 cm (super -1) which is assigned to the (super [) (super M) (super 2]) Al-O10 ->> H...O4- (super [) (super M) (super 1,3]) (Al,Fe (super 3+) ) configuration. The spectra of Sr-rich piemontites show a well-resolvable doublet at almost constant wavenumbers (3417/3454 cm (super -1) ) which can be explained by two simultaneous effects: 1) the entry of Mn (super 3+) in the non-OH-coordinated M3 octahedra and 2) the entry of Sr substituting for Ca in A2.