| Abstrakt: |
The new mineral batoniite, [Al 8 (OH) 14 (H 2 O) 18 ](SO 4)5 ⋅ 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 α= 1.4833(6), β= 1.4948(6), γ= 1.5019(5) (589 nm), and 2 V(meas.)= 71(1) ∘. Electron microprobe analysis, affected by the dehydration of batoniite under the chamber vacuum, gave (in wt %) the following: Al 2 O 3 33.48, Fe 2 O 3 0.05, SO 3 33.00, and H 2 O calc 44.41, total 110.94. It corresponds to the chemical formula (Al 7.98 Fe 0.013+)Σ7.99 (SO 4)5.01 (OH) 13.95 (H 2 O) 18 ⋅ 5H 2 O. Batoniite is triclinic, belonging to space group P1‾ , with a= 9.1757(6), b= 12.0886(9), c= 20.9218(15) Å, α= 82.901(3), β= 87.334(3), γ= 86.999(2) ∘ , V= 2297.8(3) Å 3 , and Z= 2. The crystal structure was refined to R1= 0.0916 for 8118 unique reflections with Fo>4σ(Fo) and 811 refined parameters and 60 restraints. Batoniite is characterized by isolated [Al 8 (OH) 14 (H 2 O) 18 ] 10+ polyoxocations, H-bonded to five interstitial (SO 4) 2- and five H 2 O 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 H 2 SO 4 on Al-bearing rocks of Paleozoic age cropping out in the Garibaldi Tunnel, the lowest mining level of the Cetine di Cotorniano Mine. [ABSTRACT FROM AUTHOR] |
