Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Résumé Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Hawthorne, F. C. Articles by Harlow, G. E. GeoRef GeoRef Citation

THE CRYSTAL CHEMISTRY OF Al-RICH AMPHIBOLES: SADANAGAITE AND POTASSIC-FERRISADANAGAITE

Frank C. Hawthorne^1, and George E. Harlow²

¹ Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada
² Department of Earth and Planetary Sciences, American Museum of Natural History, New York, N.Y. 10024-5192, USA

E-mail address: frank_hawthorne{at}umanitoba.ca

The crystal structures of magnesiosadanagaite (MS) from Mogok, Myanmar, monoclinic, a 9.857(2), b 17.899(4), c 5.318(1) Å, β 105.36(1)°, V 904.74(8) ų, C2/m, Z = 2, and potassic-ferrisadanagaite (FS) from the Ilmen alkaline massif, South Urals, Russia, a 9.9257(4), b 18.0917(7), c 5.3709(2) Å, β 105.19(1)°, V 930.75(2) ų, C2/m, Z = 2, have been refined to R values of ~3% using single-crystal MoK X-ray data. The crystals used in the collection of the intensity data were subsequently analyzed by electron-microprobe techniques, leading to the following compositions: MS: (Na_0.82 K_0.17) (Ca_1.95 Na_0.05) (Mg_3.36 Fe²⁺_0.23 Al_1.20 Cr³⁺_0.07 Ti⁴⁺_0.16) (Si_5.47 Al_2.53) O₂₂ [(OH)_1.58 F_0.42]; FS: (Na_0.31 K_0.62) (Ca_1.72 Na_0.28) (Mg_0.56 Fe²⁺_2.12 Mn²⁺_0.26 Zn_0.02 Al_0.72 Fe³⁺_1.07 Ti⁴⁺_0.21) (Si_5.24 Al_2.76) O₂₂ [(OH)_1.70 F_0.30]. Site populations were assigned from the results of site-scattering refinement and stereochemical analysis, taking into account the unit formula determined for each crystal. The <T–O> distances, 1.678 and 1.684 Å, indicate that ^[4]Al is strongly ordered at the T(1) site in each crystal, but the <T(2)–O> distances, 1.648 and 1.655 Å, indicate significant Al at the T(2) site. The Fe²⁺ and Fe³⁺ contents in each crystal were assigned from the <M–O> distances. The A(2) and A(m) sites are occupied by Na and (Na,K), respectively, in crystal MS, and by Na and K, respectively, in crystal FS. Both amphiboles show SRO (short-range order) of species at the M(4), O(3), A(m) and A(2) sites, and the relative abundances of these arrangements were assigned.

Keywords: amphibole, magnesiosadanagaite, potassic-ferrisadanagaite, crystal-structure refinement, electron-microprobe analysis, Mogok, Myanmar, Ilmen, South Urals, Russia.