Tripuhyite, FeSbO₄, revisited

Abstract

The exact nature of tripuhyite remains controversial more than 100 years after the first description of the mineral. Different stoichiometries and crystal structures (rutile or tri-rutile types) have been suggested for this Fe-Sb-oxide. To address these uncertainties, we studied tripuhyite from Tripuhy, Minas Gerais, Brazil (type material) and Falotta, Grisons, Switzerland using single-crystal and powder X-ray diffraction (XRD), optical microscopy and electron microprobe analysis.Electron microprobe analyses showed the Fe/Sb ratios to be close to one in tripuhyite from both localities. Single crystal XRD studies revealed that tripuhyite from the type locality and from Falotta have the rutile structure (P4 2 /mnm, a = 4.625(4) c = 3.059(5) and a = 4.6433(10) c = 3.0815(9) A Ê , respectively). Despite careful examination, no evidence for a tripled c parameter, characteristic of the tri-rutile structure, was found and hence the structure was refined with the rutile model and complete Fe-Sb disorder over the cationic sites in both cases (type material: R 1 = 3.61%; Falotta material: R 1 = 3.96%). The specular reflectance values of type material tripuhyite and lewisite were measured and the following refractive indices calculated (after Koenigsberger): tripuhyite n min = 2.14, n max = 2.27; lewisite (cubic) n = 2.04.These results, together with those of 57 Fe and 121 Sb Mössbauer spectroscopy on natural and synthetic tripuhyites reported in the literature, indicate that the chemical formula of tripuhyite is Fe 3+ Sb 5+ O 4 (FeSbO 4 ). Thus, tripuhyite can no longer be attributed to the tapiolite group of minerals of general type AB 2 O 6 . A comparison of the results presented with the mineralogical data of squawcreekite suggests that tripuhyite and squawcreekite are identical. In consequence, tripuhyite was redefined as Fe 3+ Sb 5+ O 4 with a rutile-type structure. Both the proposed new formula and unit cell (rutile-type) of tripuhyite as well as the discreditation of squawcreekite have been approved by the Commission on New Mineral and Mineral Names (CNMMN) of the International Mineralogical Association (IMA).

Quantitative antimony speciation in shooting-range soils by EXAFS spectroscopy

“…9). The distances of first (3.06-3.08 Å ) and second metal shells (3.61-3.63 Å ) reported for several tripuhyite samples are in fact similar to those of species 2 (Berlepsch et al, 2003). However, a fit of both SbAFe and SbASb backscattering paths as in tripuhyite failed, and only Fe backscattering paths could be reliably fitted.…”

“…The detail wavelet plots of the radial distances 2.4 6 r 6 3.5 Å using the optimized Morlet parameters g = 6 and r = 1 revealed only a peak at smaller k indicative of Fe, but no peak at higher k indicative of Sb for species 2, hence the presence of Sb backscatterers can be excluded (data not shown). While one could assume that the structure of species 2 represents small clusters of an Ferich tripuhyite, based on the small coordination numbers for the second metal shell and on the prevalence of Fe neighbors, the tripuhyite samples investigated by Berlepsch et al (2003) show only a small deviation from the ideal Fe-to-Sb ratio of one (site occupancy factor, SOF, of Sb: 0.47-0.53). Furthermore, our attempts to synthesize an antimonate with less Sb (SOF < 0.4) failed and led to the precipitation of Fe and Sb oxides as separate phases.…”

“…A fit with free running values for distances, coordination numbers and Debye-Waller terms resulted in physically meaningless values, requiring fit constraints. Hence the ratio of Fe/Sb coordination numbers was fixed at 1, based on the observation that the deviations from this ratio are generally to small to be detected by EXAFS-derived coordination numbers (Berlepsch et al, 2003). Furthermore, the Debye-Waller terms for both Sb shells and for both Fe shells were correlated.…”

Synthesis and characterization of new compound in the V–Fe–Sb–O system

“…The diffraction pattern of the VFeSbO 6 recorded after the final heating stage all mixtures of reagents was identical (Fig. 1d) and revealed a set of diffraction lines very similar to various diffraction patterns of phases with the rutile-type structure [26][27][28][29]. During the next stage of our research diffraction pattern of VFeSbO 6 was indexed in order to confirm the system that the compound crystallises in and determine parameters of the unit cell.…”

“…The similarity of both the powder diffraction patterns and the parameters of the unit cell and identical Miller indices (h k l) to those typical for the rutile-type of structure [26][27][28][29] indicate a possible type of structure for the new phase. This assumption was confirmed by the similarity of the IR spectra which are presented in the many papers [30][31][32].…”