Abstract
High-pressure single-crystal synchrotron X-ray diffraction data for galenobismutite, PbBi2S4 collected up to 20.9 GPa, were fitted by a third-order Birch-Murnaghan equation of state, as suggested by a FE-fE plot, yielding V0 = 697.4(8) Å3, K0 = 51(1) GPa and K’ = 5.0(2). The axial moduli were M0a = 115(7) GPa and Ma’ = 28(2) for the a axis, M0b = 162(3) GPa and Mb’ = 8(3) for the b axis, M0c = 142(8) GPa and Mc’ = 26(2) for the c axis, with refined values of a0, b0, c0 equal to 11.791(7) Å, 14.540(6) Å 4.076(3) Å, respectively, and a ratio equal to M0a:M0b:M0c = 1.55:1:1.79. The main structural changes on compression were the M2 and M3 (occupied by Bi, Pb) movements toward the centers of their respective trigonal prism bodies and M3 changes towards CN8. The M1 site, occupied solely by Bi, regularizes the octahedral form with CN6. The eccentricities of all cation sites decreased with compression testifying for a decrease in stereochemical expression of lone electron pairs. Galenobismutite is isostructural with calcium ferrite CaFe2O4, the suggested high pressure structure can host Na and Al in the lower mantle. The study indicates that pressure enables the incorporation of other elements in this structure, increasing its potential significance for mantle mineralogy.
Highlights
Galenobismutite PbBi2 S4 is a Bi-sulfosalt usually found in hydrothermal veins or associated with fumarolic deposits [1,2]
The present paper extends the study of the baric behavior of galenobismutite over a significantly larger pressure range, up to 20.9 GPa, by a synchrotron single crystal X-ray diffraction study in order to obtain a more complete picture of its behavior under high pressure
It can be visually verified by comparing the crystal a) The structural evolution is completely reversible with pressure increase up to 20.9 GPa
Summary
Galenobismutite PbBi2 S4 is a Bi-sulfosalt usually found in hydrothermal veins or associated with fumarolic deposits [1,2]. According to sulfosalt classification [3] galenobismutite is classified among commensurate composite derivatives of cannizzarite in a sub-group with angelaite, Cu2 AgPbBiS4 [4], nuffieldite, Cu1.4 Pb2.4 Bi2.4 Sb0.2 S7 [5] and weibullite, Ag0.33 Pb5.33 Bi8.33 (S,Se)18 [6] It has a distinctly different crystal structure from the chemically (stoichiometrically) similar berthierite FeSb2 S4 [7], garavellite. The reported crystal structure of NaAlSiO4 ([16], Figure 1c), obtained from a powder sample, has a substantially more distorted octahedral coordination. The present paper extends the study of the baric behavior of galenobismutite over a significantly larger pressure range, up to 20.9 GPa, by a synchrotron single crystal X-ray diffraction study in order to obtain a more complete picture of its behavior under high pressure. 4 at GPa [20]
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