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

This paper deals with a crystal-chemical, infrared spectroscopic study of monoclinic epidotes from Praborna (St. Marcel, Val d'Aosta, Italy). The studied samples range in composition from clinozoisite (Czo) to Sr-rich piemontite (Pm). In the OH-stretching region, (Al,Fe3+)-clinozoisites show a single broad band centred in the range 3345-3380 cm(-1) which is assigned to the Al-[M2]-O10-->H...O4-([M1,3])(Al,Fe3+) configuration. The spectra of Sr-rich piemontites show a well-resolvable doublet at almost constant wavenumbers (3417/3454 cm(-1)) which can be explained by two simultaneous effects: (i) the entry of Mn3+ in the non-OH-coordinated M3 octahedra acid, (ii) the entry of Sr substituting for Ca in A2.