Crystal Chemistry of Sulfates from the Apuan Alps (Tuscany, Italy). V. Scordariite, K8(Fe3+0.67□0.33)[Fe3+3O(SO4)6(H2O)3]2(H2O)11: A New Metavoltine-Related Mineral

et al. 2020

Coquimbite, AlFe3+3(SO4)6(H2O)12⋅6H2O, was considered as a pure Fe3+ hydrated sulfate. However, previous mineralogical studies pointed out the occurrence of essential Al, occupying a distinct site in the crystal structure of this mineral. Through the critical re-examination of the available literature and new crystal-chemical data collected on a specimen from the Monte Arsiccio mine, Apuan Alps, Tuscany, Italy, the chemical formula of coquimbite has been revised, taking into account the occurrence of Al. Coquimbite has a homeotypic relationship with paracoquimbite, Fe4(SO4)6(H2O)12⋅6H2O; both mineral species belong to the coquimbite group. On the contrary, aluminocoquimbite, Al2Fe2(SO4)6(H2O)12⋅6H2O, has a different topology and does not belong to that group.

Section: Coquimbite From the Monte Arsiccio Mine Apuan Alps Italymentioning

confidence: 99%

Redefinition of coquimbite, AlFe³⁺₃(SO₄)₆(H₂O)₁₂⋅6H₂O

Mauro

et al. 2020

“…In the former locality, the new mineral species volaschioite, Fe 4 (SO 4 )O 2 (OH) 6 ⋅2H 2 O, as well as Tl-bearing varieties of alum-(K) and voltaite, were found (Biagioni et al ., 2011, 2020). Moreover, Monte Arsiccio proved to be an extraordinary laboratory for the study of sulfate minerals, providing the mineral systematics with three new K–Fe sulfates (giacovazzoite, scordariite and magnanelliite – Biagioni et al ., 2019a; 2019b; 2019c), and several other species, among which were world-class specimens of coquimbite (Mauro et al ., 2020).…”

Section: Introductionmentioning

confidence: 99%

Crystal-chemistry of sulfates from the Apuan Alps, Tuscany, Italy. VIII. New data on khademite, Al(SO₄)F(H₂O)₅

Mauro

et al. 2020

Khademite, ideally Al(SO4)F(H2O)5, from the Monte Arsiccio mine, Apuan Alps, Tuscany, Italy, has been characterised through quantitative electron microprobe analysis, micro-Raman spectroscopy and single-crystal X-ray diffraction. Khademite occurs as colourless to whitish tabular crystals, up to 5 mm. Electron microprobe analysis (in wt.%, average of 20 spot analyses) gave: SO3 35.43, Al2O3 21.27, F 6.92, H2Ocalc 39.73, sum 103.35, –O = F 2.92, total 100.43. On the basis of 10 anions per formula unit, assuming the occurrence of 5 H2O groups and 1 (F+OH) atom per formula unit, its chemical formula can be written as Al0.96S1.02O4[F0.84(OH)0.16]Σ1.00⋅5H2O. The Raman spectrum of khademite is characterised by the occurrence of vibrational modes of SO4 groups and by broad and strong bands due to the O–H stretching modes. Khademite is orthorhombic, space group Pcab, with unit-cell parameters a = 11.1713(2), b = 13.0432(3), c = 10.8815(2) Å, V = 1585.54(5) Å3 and Z = 8. The crystal structure refinement converged to R1 = 0.0293 on the basis of 2359 unique reflections with Fo > 4σ(Fo) and 152 refined parameters. The crystal structure of khademite is characterised by the alternation, along b, of two distinct kinds of {010} layers, one formed by [001] rows of isolated Al-centred octahedra, connected to each other through H bonds, and the other showing isolated SO4 groups. Along b, oxygen atoms belonging to SO4 groups act as acceptor of H bonds from H2O groups coordinating Al atoms. The new data improved the description of the H bonds in khademite and led us to discuss about the possible existence of its (OH)-analogue, rostite. In addition, Raman spectroscopic data were collected on the same crystal used for the crystal-chemical characterisation, allowing a comparison with previous results.

“…Mario Bianchini provided several mineral samples for the investigation of the mineralogy of ore deposits located in the Sant'Anna tectonic window (in particular, the Pollone and Monte Arsiccio mines). He found the first specimens of the new mineral species giacovazzoite (Biagioni et al , 2020b), magnanelliite (Biagioni et al , 2019a) and scordariite (Biagioni et al , 2019b), as well as the only available material of bianchiniite (along with the mineral collector Stefano Magnanelli).…”

Section: Introductionmentioning

confidence: 99%

Bianchiniite, Ba₂(Ti⁴⁺V³⁺)(As₂O₅)₂OF, a new diarsenite mineral from the Monte Arsiccio mine, Apuan Alps, Tuscany, Italy

Hålenius

et al. 2021