Inclusive chemical characterization of tourmaline: Mössbauer study of Fe valence and site occupancy

Abstract

We report here the results of a series of inclusive chemical characterizations, including all elements except oxygen, for a suite of 54 tourmaline samples. A combination of analytical techniques was used to analyze for major and light elements (electron microprobe), Fe3 and Fe2t (Mössbauer spectroscopy), H (U extraction), and B, Li, and F (ion microprobe, or SIMS). The B content of the tourmalines studied ranges from 2.86 to 3.26 B per formula unit (pfu) with 31 anions; excess boron is believed to reside in the Si site. Li ranges from 0.0 to 1.44 Li pfu and F contents are 0.0-0.91 pfu. H contents range from nearly anhydrous up to 3.76 H pfu and do not correlate simply with Fe3t content. Mössbauer results show that tourmaline exhibits the entire range of Fe3+/2Fe from 0.0-1.0. Fe-+ is represented in the spectra by three doublets, with occupancy in at least three distinct types of Y sites (with different types of nearest and next nearest neighbors). Fe3+ was found in 26 of the 54 samples studied. Although Mössbauer data do not allow the distinction between Fe3t and