Refinement of the Crystal Structure of Ushkovite from Nevados de Palermo, República Argentina.

GALLISKI, M. A. Y HAWTHORNE, F. C.,

CANADIAN MINERALOGIST

Mineralogical Association of Canada

Lugar: Ottawa; Año: 2002 vol. 40 p. 929 - 937

0008-4476

The crystal structure of ushkovite, triclinic, a 5.3468(4), b 10.592(1), c 7.2251(7) Å,  108.278(7),  111.739(7),  71.626(7)°,V 351.55(6) Å3, Z = 2, space group P¯1, has been refined to an R index of 2.3% for 1781 observed reflections measured withMoK X-radiation. The crystal used to collect the X-ray-diffraction data was subsequently analyzed with an electron microprobe,to give the formula (Mg0.97 Mn2+0.01) (H2O)4 [(Fe3+1.99 Al0.03) (PO4) (OH) (H2O)2]2 (H2O)2, with the (OH) and (H2O) groupsassigned from bond-valence analysis of the refined structure. Ushkovite is isostructural with laueite. Chains of corner-sharing{Fe3+ O2 (OH)2 (H2O)2} octahedra extend along the c axis and are decorated by (PO4) tetrahedra to form [Fe3+2 O4 (PO4)2 (OH)2(H2O)2] chains. These chains link via sharing between octahedron and tetrahedron corners to form slabs of composition [Fe3+2(PO4)2 (OH)2 (H2O)2] that are linked by {Mg O2 (H2O)4} octahedra.Keywords: ushkovite, crystal-structure refinement, electron-microprobe analysis.