Batoniite, [Al₈(OH)₁₄(H₂O)₁₈](SO₄)₅ ⋅ 5H₂O, a new mineral with the [Al₈(OH)₁₄(H₂O)₁₈]¹⁰⁺ polyoxocation from the Cetine di Cotorniano Mine, Tuscany, Italy

Abstract. The new mineral batoniite, [Al8(OH)14(H2O)18](SO4)5 ⋅ 5H2O, was discovered in the Cetine di Cotorniano Mine, Chiusdino, Siena, Tuscany, Italy. It occurs as hemispherical aggregates composed of brittle tabular crystals, up to 1 mm size, white colorless color, with a streak and vitreous greasy luster. Batoniite is biaxial negative, α= 1.4833(6), β= 1.4948(6), γ= 1.5019(5) (589 nm), 2V(meas.)= 71(1)∘. Electron microprobe analysis, affected by dehydration batoniite under chamber vacuum, gave (in wt %) following: Al2O3 33.48, Fe2O3 0.05, SO3 33.00, H2Ocalc 44.41, total 110.94. corresponds chemical formula (Al7.98Fe0.013+)Σ7.99(SO4)5.01(OH)13.95(H2O)18 5H2O. triclinic, belonging space group P1‾, a= 9.1757(6), b= 12.0886(9), c= 20.9218(15) Å, 82.901(3), 87.334(3), 86.999(2)∘, V= 2297.8(3) Å3, Z= 2. crystal structure refined R1= 0.0916 for 8118 unique reflections Fo>4σ(Fo) 811 parameters 60 restraints. characterized isolated [Al8(OH)14(H2O)18]10+ polyoxocations, H-bonded five interstitial (SO4)2− H2O groups. In type material, it associated gypsum poorly crystallized Al–Fe sulfate. crystallization probably due action H2SO4 on Al-bearing rocks Paleozoic age cropping out Garibaldi Tunnel, lowest mining level Mine.