The crystal structures of a suite of amphiboles from the Kola Superdeep Borehole, Russia, have been refined to R values of ∼3% using single-crystal Mo-Kα X-ray diffraction data. The same crystals used in the collection of the intensity data were subsequently analysed by electron microprobe (EMP) and milliprobe Mössbauer spectroscopy. Site populations were assigned from the results of site-scattering refinement and stereochemical analysis, taking into account the unit formula determined for each crystal. The Fe3+/(Fe2++Fe3+) values were derived (1) by least-squares refinement of the Mössbauer spectra, and (2) SREF (Structure REFinement) by careful analysis of the mean bond lengths at the M(2) site using two possible models for the behaviour of Ti4+: (i) Ti4+ at M(2); and (ii) Ti4+ at M(1). The agreement between the SREF and Mössbauer/EMP values for Fe3+ is very close for Ti4+ assigned to M(2). This result indicates that the calculation of Fe3+ contents in amphiboles from refined site populations and <M(2)–O> distances are accurate. This paper presents the first confirmation of this result.
