Abstract
The new mineral species scordariite, K8(Fe3+0.67□0.33)[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+0.67□0.33)[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.
Highlights
In the last decade, the Monte Arsiccio mine has been studied for its interesting sulfosalt assemblages (e.g., Biagioni et al [1]) and the occurrence of some very peculiar oxides
Sulfate assemblages deriving from the weathering of pyrite ores have been investigated, leading to the description of three new mineral species: giacovazzoite [4], magnanelliite [5], and scordariite
Minerals 2019, 9, 702 through energy-dispersive X-ray spectrometry and X-ray powder diffraction confirmed the distinction between monoclinic giacovazzoite, the natural analogue of β-Maus’ salt [4], and the new mineral scordariite
Summary
The Monte Arsiccio mine has been studied for its interesting sulfosalt assemblages (e.g., Biagioni et al [1]) and the occurrence of some very peculiar oxides (e.g., mannardite [2], mapiquiroite [3]). Sulfate assemblages deriving from the weathering of pyrite ores have been investigated, leading to the description of three new mineral species: giacovazzoite [4], magnanelliite [5], and scordariite. All these new species are K–Fe3+ sulfates, likely deriving from the interaction between acidic solutions and K-bearing rocks. Fernando Scordari is the author of more than 150 papers and three textbooks about crystallography and mass spectrometry His scientific activity was devoted to the crystal chemistry of minerals and inorganic compounds, with a particular focus on silicates and sulfates. This paper presents the definition, occurrence, and crystal structure of the new mineral species scordariite
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