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Vesuvianite from the Somma-Vesuvius Complex: New Data and Revised Formula

Taras L. Panikorovskii 1,2, Nikita V. Chukanov 3, Vyacheslav S. Rusakov 4 , Vladimir V. Shilovskikh 5, Anton S. Mazur 6, Giuseppina Balassone 7 , Gregory Yu. Ivanyuk 2 and Sergey V. Krivovichev 1,2

Minerals 2017, 7, 248

1 Department of Crystallography, Institute of Earth Sciences, St. Petersburg State University, University Embankment, 7/9, St. Petersburg 199034, Russia; s.krivovichev@spbu.ru
2 Kola Science Centre, Russian Academy of Sciences, 14 Fersman Street, Apatity 184200, Russia; ivanyuk@admksc.apatity.ru
3 Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka 142432, Russia; chukanov@icp.ac.ru
4 Faculty of Physics, Moscow State University, Vorobievy Gory, Moscow 119991, Russia; rusakov@phys.msu.ru
5 Department of Colloid Chemistry, Insitute of Chemistry, St. Petersburg State University, University Av. 26, St. Petersburg 198504, Russia; vova_bel@mail.ru
6 Center for Magnetic Resonance, St. Petersburg State University, University Av. 26, St. Petersburg 198504, Russia; a.mazur@spbu.ru
7 Dipartimento di Scienze della Terra, dell’Ambiente e delle Risorse, Università degli Studi di Napoli Federico II, Compless Universitario Monte S. Angelo, Via Cinthia 26, 80126 Napoli, Italy; balasson@unina.it
At present, the vesuvianite group of minerals consists of eight members, six of which are distinguished by the dominant cation in the Y1(A,B) five-coordinated site. We investigated two vesuvianite samples from the type locality by electron microprobe analysis, Mössbauer and infrared spectroscopy, TGA/DSC, MAS NMR, single-crystal and powder X-ray diffraction.
The crystal structures of these samples (# 27844 and 51062 from the Vesuvius collection, Fersman Mineralogical Museum, Moscow) have been refined to R1 = 0.027 and R1 = 0.035, respectively.
Both samples have the space group P4/nnc; a = 15.5720(3) and 15.5459(3), c = 11.8158(5) and 11.7988(4), respectively. In both samples low-occupied T1 and T2 sites are populated by minor B and Al, which agrees with their high-temperature origin. According to our experimental results, the general revised crystal-chemical formula of vesuvianite can be written as VIII-IX X19 VY1 VIY12(Z2O7)4(ZO4)10(W)10, where X are sevento nine-coordinated sites of Ca with minor Na, K, Fe2+ and REE impurities; VY has a square pyramidal coordination and is occupied predominantly by Fe3+ with subordinate Mg, Al, Fe2+ and Cu2+; VIY has octahedral coordination and is predominantly occupied by Al with subordinate Mg, Fe2+, Fe3+, Mn2+, Mn3+, Ti, Cr and Zn; ZO4 = SiO4, sometimes with subordinate AlO4 and/or (OH)4, and W = OH, F, with minor O and Cl. The idealized charge-balanced formula of the vesuvianite end-member without subordinate cations is Ca19Fe3+(Al10Me2+ 2)(Si2O7)4(SiO4)10O(OH)9, where Me = Fe2+, Mg2+, Mn2+.
Keywords: vesuvianite-group minerals; Somma-Vesuvius volcanic complex; vesuvianite; nomenclature; crystal structure