Galliskiite, Ca4Al2(PO4)2F8•5H2O, a new mineral from the Gigante granitic pegmatite, Cordoba province, Argentina

Galliskiite, idcally Ca4Al2(PO4)(2)F-8 center dot 5H(2)O. is a new mineral found at the Gigante granitic pegmatite, Punilla department. Cordoba Province, Argentina. It is named for Argentine mineralogist and pegmatite specialist Miguel Angel Galliski. Galliskiite is triclinic, P (1) over bar, a=6.1933(7), b=9.871(i), c= 13.580(2) angstrom, alpha =89.716(3), beta = 75.303(4), gamma = 88.683(4)degrees, Z = 2. The strongest lines in the X-ray powder diffraction pattern are [(d in angstrom (I)]: 7.904 (70), 5.994 (100), 3.280 (58), 3.113 (30), 2.945 (85), 2.887 (44), 2.483 (20) 2.262 (27), 2.150 (23) 1.821 (27) and 1.798 (25). It occurs as crude platy crystals elongated along [001] and flattened on {010}, With frosty surface. Simple contact and polysynthetic twinning on 1001 by rotation about [010] is ubiquitous. It is colorless and transparent. has white streak and vitreous luster, and is nonfluorescent under Ultraviolet radiation. It has a Molls hardness of 21/2, conchoidal to irregular fracture and two fair cleavages at approximately 90 degrees. The measurement density is 2.67(3) g/cm(3), and the calculated density is 2.670 g/cm(3). Galliskiite dissolves slowly in concentrated HCl. The mineral is biaxial (+), alpha = 1.493(1) beta = 1.495(1) gamma= 1.520(1) 2V(meas)= 33(5)degrees 2V(cat) = 32 degrees, dispersion, r < v, orientation Z approximate to b. X and Z at 40-50 degrees from a and c. No pleochroism is observed. Analysis by electron microprobe (average of 12 analyses given in wt%) provided CaO 34.71, MgO 0.01, FeO 0.10 MnO 0.17, Al2O3 15.92, SiO2 0.06 TiO2 0.01. P2O5 21.94, F 21.35, H2O (calculated by stoichiometry) 15.08, less F O 8.99, total 100.39 wt%. The empirical formula. based on 21 (17+% is (Ca3.98Mn0.02Fe0.01)(Sigma 4.0)Al-2.01(P1.99Si0.01)F-7.23(OH)(0.77)center dot 5H(2)O. The crystal structure, solved and refined using single-crystal data to R-1 = 0.033, consists of double chains of alternating corner-sharing AlF3O3 octahedra and PO, tetrahedra along the a axis. The chains are joined into a framework via bonds to four distinct Ca atoms. Calcium atoms are also linked by sharing isolated F atoms and H2O molecules. The double-chain motif in the structure of galliskiite is distinct front that in any other known phosphate.