Vesuvianite from the Somma-Vesuvius Complex: New data and revised formula

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Marco E. Ciriotti
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Vesuvianite from the Somma-Vesuvius Complex: New data and revised formula

Messaggio da Marco E. Ciriotti » sab 16 dic, 2017 12:17

Referenza:
▪ Panikorovskii, T.L., Chukanov, N.V., Rusakov, V.S., Shilovskikh, V.V., Mazur, A.S., Balassone, G., Ivanyuk, G.Yu., Krivovichev, S.V. (2017): Vesuvianite from the Somma-Vesuvius Complex: New Data and Revised Formula. Minerals, 7, 248; doi:10.3390/min7120248.

Abstract:
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 VII−IXX19VY1VIY12(Z2O7)4(ZO4)10(W)10, where X are seven- to 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 Ме = Fe2+, Mg2+, Mn2+.

NdR:
1. Formula generale gruppo vesuvianite:
X16X12X4Y1Y24Y38T0–5(Z2O7)4[(ZO4)10􀀀x(H4O4)x](W)9O1–3, where x < 3, X are seven- to nine-coordinated sites (Ca, Na, K, Fe2+, REE), X4 has square antiprismatic coordination (Ca, Na), Y1 has square pyramidal coordination (Fe3+, Mg, Al, Fe2+, Cu2+), Y2 and Y3 have octahedral coordination (Al, Mg, Zn, Fe2+, Fe3+, Mn2+, Mn3+, Ti, Cr, Zn), T is the additional site with triangular or tetrahedral coordination (B, Fe), ZO4 [SiO4, , (OH)4, AlO4] and Z2O7 (Si2O7) and the additional anionic position W can be occupied by OH, F, or minor O, Cl.

2. La formula della vesuvianite (s.s.) e quindi anche quella della località-tipo può essere esposta con: Ca19Fe3+Al10(Mg,Fe2+)2(Si2O7)4(SiO4)10O(OH)9.

3. Trattandosi di un articolo open access è possibile scaricare gratuitamente (e vi invito a farlo) l'intero testo: http://www.mdpi.com/2075-163X/7/12/248
Marco E. Ciriotti

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