Rosenbergite, AlF[F (sub 0.5) (H (sub 2) O) (sub 0.5) ] (sub 4) .H (sub 2) O, a new mineral from the Cetine Mine (Tuscany, Italy); description and crystal structure

Rosenbergite occurs as radiating tufts of slender tetragonal crystals, elongated on [001], in cavities in a highly silicified limestone, in association with gypsum, fluorite, elpasolite, ralstonite and onoratoite. It is colourless and transparent, with a vitreous lustre; epsilon 1.403, omega 1.427; VHN (sub 15) 103, D 2.10 g/cm (super 3) . Indexed XRD powder data are tabulated; strongest lines 5.47(100), 1.725(85), 1.775(78), 2.027(70), 1.306(70) Angstrom ; a 7.715, c 3.648; space group P4/n; Z = 2. EPMA (H (sub 2) O by difference) gave Al (sub 1.02) F (sub 2.98) bullet 2.99H (sub 2) O, or ideally AlF (sub 3) bullet 3H (sub 2) O; the IR spectrum is also given. The crystal structure was refined to R 0.0186, and consists of chains of corner-linked Al[(F (sub 4) (H (sub 2) O) (sub 2) ] octahedra [001] and isolated water molecules; a dense network of hydrogen bonds connects the Al-F chains.