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Minerals 2018, 8(4), 152; https://doi.org/10.3390/min8040152

Tiberiobardiite, Cu9Al(SiO3OH)2(OH)12(H2O)6(SO4)1.5·10H2O, a New Mineral Related to Chalcophyllite from the Cretaio Cu Prospect, Massa Marittima, Grosseto (Tuscany, Italy): Occurrence and Crystal Structure

1
Dipartimento di Scienze della Terra, Università di Pisa, Via Santa Maria 53, I-56126 Pisa, Italy
2
Department of Applied Geological Sciences and Geophysics, University of Leoben, Peter Tunner Str. 5, A-8700 Leoben, Austria
*
Author to whom correspondence should be addressed.
Received: 23 March 2018 / Revised: 6 April 2018 / Accepted: 9 April 2018 / Published: 11 April 2018
(This article belongs to the Special Issue New Mineral Species and Their Crystal Structures)
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Abstract

The new mineral species tiberiobardiite, ideally Cu9Al(SiO3OH)2(OH)12(H2O)6(SO4)1.5·10H2O, has been discovered in the Cretaio Cu prospect, Massa Marittima, Grosseto, Tuscany, Italy, as very rare, light green, vitreous, tabular {0001}, pseudo-hexagonal crystals, up to 200 μm in size and 5 μm in thickness, associated with brochantite. Electron microprobe analysis gave (in wt %, average of 5 spot analyses): SO3 10.37, P2O5 3.41, As2O5 0.05, SiO2 8.13, Al2O3 5.54, Fe2O3 0.74, CuO 62.05, and ZnO 0.03, for a total of 90.32. Based on an idealized O content of 42 atoms per formula unit, assuming the presence of 16 H2O groups and 13.5 cations (without H), the empirical formula of tiberiobardiite is (Cu8.69Al0.21Fe0.10)Σ9.00Al1.00(Si1.51P0.54)Σ2.05S1.44O12.53(OH)13.47·16H2O. The main diffraction lines, corresponding to multiple hkl indices, are [d in Å (relative visual intensity)]: 9.4 (s), 4.67 (s), 2.576 (m), 2.330 (m), and 2.041 (mw). The crystal structure study revealed tiberiobardiite to be trigonal, space group R 3 ¯ , with unit-cell parameters a = 10.6860(4), c = 28.3239(10) Å, V = 2801.0(2) Å3, and Z = 3. The crystal structure was refined to a final R1 = 0.060 for 1747 reflections with Fo > 4σ (Fo) and 99 refined parameters. Tiberiobardiite is the Si-analogue of chalcophyllite, with Si4+ replacing As5+ through the coupled substitution As5+ + O2− = Si4+ + (OH). The name tiberiobardiite honors Tiberio Bardi (b. 1960) for his contribution to the study of the mineralogy of Tuscany. View Full-Text
Keywords: tiberiobardiite; chalcophyllite group; copper; silicate; sulfate; Cretaio; Tuscany; Italy tiberiobardiite; chalcophyllite group; copper; silicate; sulfate; Cretaio; Tuscany; Italy
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Biagioni, C.; Pasero, M.; Zaccarini, F. Tiberiobardiite, Cu9Al(SiO3OH)2(OH)12(H2O)6(SO4)1.5·10H2O, a New Mineral Related to Chalcophyllite from the Cretaio Cu Prospect, Massa Marittima, Grosseto (Tuscany, Italy): Occurrence and Crystal Structure. Minerals 2018, 8, 152.

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