Rosenbergite, AlF[F0.5(H2O)0.5]4·H2O, a new mineral from the Cetine mine (Tuscany, Italy): description and crystal structure
Olmi, Filippo; Sabelli, Cesare; Trosti-Ferroni, Renza
European Journal of Mineralogy Volume 5 Number 6 (1993), p. 1167 - 1174
published: Dec 1, 1993
manuscript accepted: Jun 23, 1993
manuscript received: Mar 18, 1993
ArtNo. ESP147050506010, Price: 29.00 €
Abstract Rosenbergite is a new aluminium fluoride mineral from the Cetine mine, Tuscany, Italy. It occurs as radiating tufts of slender tetragonal crystals, elongated parallel to , in cavities in a highly silicified limestone. The crystals are colourless and transparent, with a vitreous lustre. Associated minerals are gypsum, fluorite, elpasolite, ralstonite and onoratoite. Electron microprobe analysis (water by difference) gives AI1.02F22.214.171.124H2O (simplified formula AIF3.3H2O). Optically uniaxial (-) with ⋲ = 1.403 and ω = 1.427; VHN15 microhardness 103; dcalc = 2.111 g/cm3; dmeas = 2.10(l)g/cm3. The unit cell is tetragonal a = 7.715(1), c = 3.648(1)Å, space group P4/n and Z = 2. The strongest lines in the X-ray Gandolfi pattern are (dobs,I,hkl) 5.47(100)(110), 2.439(72)(130), 2.027(70)(131), 1.775(78)(012), 1.725(85)(240), 1.306(70)(142). The IR spectrum is also given. The mineral is named for P.E. Rosenberg of Washington State University, U.S.A. The crystal structure was refined to an R index of 0.0186, using a set of 245 observed (16 α) reflections (R = 0.0276 for all 316 collected reflections). The structure consists of chains of corner-linked A1[F4(H2O)2] octahedra running parallel to  and isolated water molecules. A dense network of hydrogen bonds strongly connects the Al-F chains. The structural formula is AlF[F0.5(H2O)0.5]4.H2O.