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Crystal Chemistry of Sulfates from the Apuan Alps (Tuscany, Italy). V. Scordariite, K8(Fe3+0.670.33)[Fe3+3O(SO4)6(H2O)3]2(H2O)11: A New Metavoltine-Related Mineral

1
Dipartimento di Scienze della Terra, Università di Pisa, Via Santa Maria 53, I-56126 Pisa, Italy
2
Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Via G. La Pira 4, I-50121 Firenze, Italy
3
Department of Geosciences, Swedish Museum of Natural History, Box 50007, SE-10405 Stockholm, Sweden
*
Author to whom correspondence should be addressed.
Minerals 2019, 9(11), 702; https://doi.org/10.3390/min9110702
Received: 30 October 2019 / Revised: 8 November 2019 / Accepted: 11 November 2019 / Published: 13 November 2019
(This article belongs to the Collection New Minerals)
The new mineral species scordariite, K8(Fe3+0.670.33)[Fe3+3O(SO4)6(H2O)3]2(H2O)11, was discovered in the Monte Arsiccio mine, Apuan Alps, Tuscany, Italy. It occurs as pseudo-hexagonal tabular crystals, yellowish to brownish in color, up to 0.5 mm in size. Cleavage is perfect on {0001}. It is associated with giacovazzoite, krausite, gypsum, jarosite, alum-(K), and magnanelliite. Electron microprobe analyses give (wt %): SO3 47.31, Al2O3 0.66, Fe2O3 24.68, FeO 0.69, Na2O 0.52, K2O 17.36, H2Ocalc 15.06, total 106.28. The partitioning of Fe between Fe2+ and Fe3+ was based on Mössbauer spectroscopy. On the basis of 67 O atoms per formula unit, the empirical chemical formula is (K7.50Na0.34)Σ7.84(Fe3+6.29Al0.26Fe2+0.20)Σ6.75S12.02O50·17H2O. The ideal end-member formula can be written as K8(Fe3+0.670.33)[Fe3+3O(SO4)6(H2O)3]2(H2O)11. Scordariite is trigonal, space group R-3, with (hexagonal setting) a = 9.7583(12), c = 53.687(7) Å, V = 4427.4(12) Å3, Z = 3. The main diffraction lines of the observed X-ray powder pattern are [d(in Å), estimated visual intensity]: 8.3, strong; 6.6, medium; 3.777, medium; 3.299, medium; 3.189, medium; 2.884, strong. The crystal structure of scordariite has been refined using X-ray single-crystal data to a final R1 = 0.057 on the basis of 1980 reflections with Fo > 4σ(Fo) and 165 refined parameters. It can be described as a layered structure formed by three kinds of layers. As with other metavoltine-related minerals, scordariite is characterized by the occurrence of the [Fe3+3O(SO4)6(H2O)3]5− heteropolyhedral cluster. View Full-Text
Keywords: scordariite; new mineral species; sulfate; potassium; iron; crystal structure; Monte Arsiccio mine; Apuan Alps; Italy scordariite; new mineral species; sulfate; potassium; iron; crystal structure; Monte Arsiccio mine; Apuan Alps; Italy
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Biagioni, C.; Bindi, L.; Mauro, D.; Hålenius, U. Crystal Chemistry of Sulfates from the Apuan Alps (Tuscany, Italy). V. Scordariite, K8(Fe3+0.670.33)[Fe3+3O(SO4)6(H2O)3]2(H2O)11: A New Metavoltine-Related Mineral. Minerals 2019, 9, 702.

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