The new mineral nannoniite, Al2(OH)5F (Z = 4), has been discovered in the Cetine di Cotorniano mine, Chiusdino, Siena, Tuscany, Italy. It occurs as spherical aggregates formed by micrometre-sized crystals, colourless to white in colour, with a white streak and a vitreous to earthy lustre. Fluorescence is bluish-yellow and yellowish-white under short- and longwave UV radiation, respectively. Electron microprobe analysis gave (in wt %) SO3 0.49, Al2O3 63.97, MgO 0.51, CaO 0.22, K2O 0.07, F 11.72, H2O(calc) 28.54, and -O = F - 4.94, with a total of 100.58. Nannoniite is monoclinic, with space group P21/n and with a = 8.688(3), b = 5.024(2), c = 9.734(4) Å,  D 90.77(2)°, and V = 424.9(3)Å3. The crystal structure was solved using three-dimensional electron diffraction and refined to R(obs) = 0.1524 for 2141 unique reflections with I > 3σ(I). Nannoniite is homeotypic with gibbsite. In type material, nannoniite is associated with quartz, baryte, gypsum, and alunite in vugs of a silicified limestone. Its origin is probably related to the late-stage circulation of (Al,F)-rich fluids within the Sb ore deposit formerly exploited at the Cetine di Cotorniano mine.
Nannoniite, Al2(OH)5F, a new mineral from the Cetine di Cotorniano mine (Tuscany, Italy)
Belmonte D.;
2024-01-01
Abstract
The new mineral nannoniite, Al2(OH)5F (Z = 4), has been discovered in the Cetine di Cotorniano mine, Chiusdino, Siena, Tuscany, Italy. It occurs as spherical aggregates formed by micrometre-sized crystals, colourless to white in colour, with a white streak and a vitreous to earthy lustre. Fluorescence is bluish-yellow and yellowish-white under short- and longwave UV radiation, respectively. Electron microprobe analysis gave (in wt %) SO3 0.49, Al2O3 63.97, MgO 0.51, CaO 0.22, K2O 0.07, F 11.72, H2O(calc) 28.54, and -O = F - 4.94, with a total of 100.58. Nannoniite is monoclinic, with space group P21/n and with a = 8.688(3), b = 5.024(2), c = 9.734(4) Å, D 90.77(2)°, and V = 424.9(3)Å3. The crystal structure was solved using three-dimensional electron diffraction and refined to R(obs) = 0.1524 for 2141 unique reflections with I > 3σ(I). Nannoniite is homeotypic with gibbsite. In type material, nannoniite is associated with quartz, baryte, gypsum, and alunite in vugs of a silicified limestone. Its origin is probably related to the late-stage circulation of (Al,F)-rich fluids within the Sb ore deposit formerly exploited at the Cetine di Cotorniano mine.
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