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The occurrence of sulfate minerals associated with the pyrite ores of the southern Apuan Alps has been known since the 19th century but modern mineralogical studies started only in the last decade. Sulfate assemblages were identified in all the pyrite ore deposits from the studied area but the more impressive associations were discovered in the Fornovolasco and Monte Arsiccio mines. Their study allowed to improve the knowledge of the sulfate crystal-chemistry and to achieve a better understanding of the acid mine drainage (AMD) systems associated with pyrite oxidation. More than 20 different mineral species were identified and, among them, four sulfates (volaschioite, giacovazzoite, magnanelliite, and scordariite) have their type localities in the pyrite ore deposits of the Apuan Alps. A review of the mineralogical results of a ten-year-long study is given here. Full article

The new mineral species magnanelliite, K₃Fe³⁺₂(SO₄)₄(OH)(H₂O)₂, was discovered in the Monte Arsiccio mine, Apuan Alps, Tuscany, Italy. It occurs as steeply terminated prisms, up to 0.5 mm in length, yellow to orange-yellow in color, with a vitreous luster. Streak is pale yellow, Mohs hardness is ca. 3, and cleavage is good on {010}, fair on {100}. The measured density is 2.82(3) g/cm³. Magnanelliite is optically biaxial (+), with α = 1.628(2), β = 1.637(2), γ = 1.665(2) (white light), 2V_meas = 60(2)°, and 2V_calc = 59.9°. It exhibits a strong dispersion, r > v. The optical orientation is Y = b, X ^ c ~ 25° in the obtuse angle β. It is pleochroic, with X = orange yellow, Y and Z = yellow. Magnanelliite is associated with alum-(K), giacovazzoite, gypsum, jarosite, krausite, melanterite, and scordariite. Electron microprobe analyses give (wt.%): SO₃ 47.82, TiO₂ 0.05, Al₂O₃ 0.40, Fe₂O₃ 25.21, MgO 0.07, Na₂O 0.20, K₂O 21.35, H₂O_calc 6.85, total 101.95. On the basis of 19 anions per formula unit, assuming the occurrence of one (OH)⁻ and two H₂O groups, the empirical chemical formula of magnanelliite is (K_2.98Na_0.04)_Σ3.02(Fe³⁺_2.08Al_0.05Mg_0.01)_Σ2.14S_3.93O₁₆(OH)(H₂O)₂. The ideal end-member formula can be written as K₃Fe³⁺₂(SO₄)₄(OH)(H₂O)₂. Magnanelliite is monoclinic, space group C2/c, with a = 7.5491(3), b = 16.8652(6), c = 12.1574(4) Å, β = 94.064(1)°, V = 1543.95(10) ų, Z = 4. Strongest diffraction lines of the observed X-ray powder pattern are [d(in Å), estimated visual intensity, hkl]: 6.9, medium, 021 and 110; 4.91, medium-weak, 022; 3.612, medium-weak, $\overline{1}$ 32, 023, and $\overline{1}$ 13; 3.085, strong, 202, 150, and $\overline{1}$ 33; 3.006, medium, 004, $\overline{1}$ 51, and 151; 2.704, medium, 152 and $\overline{2}$ 23; 2.597, medium-weak, $\overline{2}$ 42; 2.410, medium-weak, 153. The crystal structure of magnanelliite has been refined using X-ray single-crystal data to a final R₁ = 0.025, on the basis of 2411 reflections with F_o > 4σ(F_o) and 144 refined parameters. The crystal structure is isotypic with that of alcaparrosaite, K₃Ti⁴⁺Fe³⁺(SO)₄O(H₂O)₂. Full article

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, H₂O_calc 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 (K_7.50Na_0.34)_Σ7.84(Fe³⁺_6.29Al_0.26Fe²⁺_0.20)_Σ6.75S_12.02O₅₀·17H₂O. 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) ų, 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 F_o > 4σ(F_o) 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. Full article