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@article{2355381,
author = {Bačík, Peter and Wildner, Manfred and Cempírek, Jan and Škoda, Radek and Cibula, Peter and Vaculovič, Tomáš},
article_number = {4},
doi = {http://dx.doi.org/10.1180/mgm.2023.48},
keywords = {zoisite; vanadium; octahedron; optical absorption spectroscopy; crystal field Superposition Model; bond-valence calculation},
language = {eng},
issn = {0026-461X},
journal = {Mineralogical Magazine},
title = {The position of vanadium in the crystal structure of zoisite, variety tanzanite: Structural refinement, optical absorption spectroscopy and bond-valence calculations},
url = {https://doi.org/10.1180/mgm.2023.48},
volume = {87},
year = {2023}
}
TY - JOUR
ID - 2355381
AU - Bačík, Peter - Wildner, Manfred - Cempírek, Jan - Škoda, Radek - Cibula, Peter - Vaculovič, Tomáš
PY - 2023
TI - The position of vanadium in the crystal structure of zoisite, variety tanzanite: Structural refinement, optical absorption spectroscopy and bond-valence calculations
JF - Mineralogical Magazine
VL - 87
IS - 4
SP - 599-610
EP - 599-610
PB - Mineralogical Society
SN - 0026461X
KW - zoisite
KW - vanadium
KW - octahedron
KW - optical absorption spectroscopy
KW - crystal field Superposition Model
KW - bond-valence calculation
UR - https://doi.org/10.1180/mgm.2023.48
N2 - Vanadium is the dominant trace element and chromophore in tanzanite, the most valued gemmological variety of zoisite. The structure of zoisite–tanzanite was obtained by structural refinement to assess the vanadium location in the zoisite structure. However, the small V content in tanzanite evidenced by electron microprobe and laser ablation inductively coupled plasma mass spectrometry limits the exact determination of the V position in the zoisite structure. Structural refinement revealed that the average bond length of the less distorted M1,2O6 octahedron is below 1.90 Å, and M3O6 has slightly longer bonds with an average of ca. 1.96 Å. The M1,2 site is slightly overbonded with a bond-valence sum (BVS) of 3.03 vu, whereas M3 is slightly underbonded (BVS = 2.78 vu). Optical absorption spectra revealed that most V is trivalent, but a small portion is probably in a four-valent state. Therefore, crystal field Superposition Model and Bond-Valence Model calculations were applied based on several necessary assumptions: (1) V occupies octahedral sites; and (2) it can occur in two oxidation states, V3+ or V4+. Crystal field Superposition Model calculations from the optical spectra indicated that V3+ prefers occupying the M1,2 site; the preference of V4+ from the present data was impossible to determine. Bond-Valence Model calculations revealed no unambiguous preference for V3+, although simple bond-length calculation suggests the preference of the M3 site. However, it is quite straightforward that the M1,2 site is better suitable for V4+. If the possible octahedral distortion is considered, the M1,2O6 octahedron is subject to a smaller change in distortion if occupied by V3+ than the M3O6 octahedron. Consequently, considering the results of both the crystal field Superposition Model and Bond-Valence Model calculations, we assume that both V3+ and V4+ prefer the M1,2 site.
ER -
BAČÍK, Peter, Manfred WILDNER, Jan CEMPÍREK, Radek ŠKODA, Peter CIBULA a Tomáš VACULOVIČ. The position of vanadium in the crystal structure of zoisite, variety tanzanite: Structural refinement, optical absorption spectroscopy and bond-valence calculations. \textit{Mineralogical Magazine}. Mineralogical Society, 2023, roč.~87, č.~4, s.~599-610. ISSN~0026-461X. Dostupné z: https://dx.doi.org/10.1180/mgm.2023.48.
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