Carlhintzeite, Ca2AlF7?H2O, from the Gigante granitic pegmatite, Córdoba province, Argentina: Description and crystal structure.

KAMPF, ANTHONY R.; COLOMBO, FERNANDO; GONZÁLEZ DEL TÁNAGO, JOSÉ

MINERALOGICAL MAGAZINE

MINERALOGICAL SOC

Lugar: Middlesex; Año: 2010 vol. 74 p. 623 - 632

0026-461X

<!-- /* Font Definitions */ @font-face {font-family:TimesNewRoman; panose-1:0 0 0 0 0 0 0 0 0 0; mso-font-alt:"Times New Roman"; mso-font-charset:0; mso-generic-font-family:roman; mso-font-format:other; mso-font-pitch:auto; mso-font-signature:131 0 0 0 9 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:ES-AR;} @page Section1 {size:595.3pt 841.9pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:35.4pt; mso-footer-margin:35.4pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Carlhintzeite, Ca2AlF7·H2O, has been found at the Gigante pegmatite, Punilla Department, Córdoba Province, Argentina. It occurs as colorless prismatic crystals up to 0.8 mm long, ubiquitously twinned on {001}. Electron microprobe analyses provided the empirical formula Ca1.98Al1.02F6.24(OH)0.76·H1.62O. A crystal fragment used for the collection of structure data provided the triclinic, C-1 cell: a = 9.4227(4), b = 6.9670(5), c = 9.2671(7) Å, α = 90.974(6), β = 04.802(5), γ = 90.026(6)°, V = 558.08(7) Å3 and Z = 4. The crystal structure, solved by direct methods and refined to R1 = 0.0322 for 723 Fo > 4sF reflections, is made up of linkages of AlF6 octahedra, CaF8 polyhedra and CaF6(H2O)2 polyhedra. The AlF6 octahedra are isolated from one another, but share polyhedral elements with Ca polyhedra. Most notably, the Al1 octahedron shares trans faces with two CaF8 polyhedra and the Al2 octahedron shares trans edges with two CaF6(H2O)2 polyhedra. The linkage of the Ca polyhedra alone can be described as a framework in which edge-sharing chains along b are cross-linked by edge-sharing. Edge-sharing chains of Ca polyhedra along b in the carlhintzeite structure are similar to those along c in the structures of gearksutite, CaAlF4(OH)·(H2O), and prosopite, CaAl2F4(OH)4.