Batoniite, [Al₈(OH)₁₄(H₂O)₁₈](SO_{4< /sub>)5 ? 5H2O, a new mineral with the [Al8(OH)14(H2O)18]^{10+ polyoxocation from the Cetine di Cotorniano Mine, Tuscany, Italy}}

The new mineral batoniite, [Al-8(OH)(14)(H2O)(18)](SO4)(5) & sdot; 5H(2)O, 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 in size, white to colorless in color, with a white streak and a vitreous to greasy luster. Batoniite is biaxial negative, with alpha= 1.4833(6), beta= 1.4948(6), gamma= 1.5019(5) (589 nm), and 2V ((meas)) 71(1)(degrees). Electron microprobe analysis, affected by the dehydration of batoniite under the chamber vacuum, gave (in wt %) the following: Al2O3 33.48, Fe2O3 0.05, SO3 33.00, and H2Ocalc 44.41, total 110.94. It corresponds to the chemical formula (Al7.98Fe(SO4)(5.01)(OH)(13.95)(H2O)(18) & sdot; 5H(2)O. Batoniite is triclinic, belonging to space group , with a= 9.1757(6), b= 12.0886(9), c= 20.9218(15) & Aring;, alpha= 82.901(3), beta= 87.334(3), gamma= 86.999(2)(degrees), V= 2297.8(3) & Aring;(3), and Z= 2. The crystal structure was refined to R-1= 0.0916 for 8118 unique reflections with F-o>4 sigma(F-o) and 811 refined parameters and 60 restraints. Batoniite is characterized by isolated [Al-8(OH)(14)(H2O)(18)](10+) polyoxocations, H-bonded to five interstitial (SO4)(2-) and five H2O groups. In type material, it is associated with gypsum and a poorly crystallized Al-Fe sulfate. The crystallization of batoniite is probably due to the action of H2SO4 on Al-bearing rocks of Paleozoic age cropping out in the Garibaldi Tunnel, the lowest mining level of the Cetine di Cotorniano Mine.