Can I read Si, Al ordering in the double-ring silicate armenite, BaCa~2~Al~6~Si~9~O~30~.2H~2~O; a single-crystal X-ray and^29^Si MAS NMR study on EtoBox?

Si, Al ordering in the double-ring silicate armenite, BaCa~2~Al~6~Si~9~O~30~.2H~2~O; a single-crystal X-ray and^29^Si MAS NMR study by Thomas Armbruster is a Earth and Planetary Sciences article available to read on EtoBox.

What is Si, Al ordering in the double-ring silicate armenite, BaCa~2~Al~6~Si~9~O~30~.2H~2~O; a single-crystal X-ray and^29^Si MAS NMR study about?

The 29 Si MAS NMR spectrum of armenite from Wasenalp (Valais, Switzerland) indicates complete Si, Al ordering. The same chemical shifts (Ϫ82.3, Ϫ95.0, and Ϫ101.8 ppm) were also measured for armenite from Re ́migny (Quebec, Canada), however, the intensity ratios of the NMR bands for the latter sample differed. A full sphere of X-ray single-crystal data on an optically homogeneous domain of armenite from Re ́migny was collected on a threecircle diffractometer equipped with a CCD area-detector. The crystal structure was refined in the acentric space group Pnc2 [a ϭ 18.660(2), b ϭ 10.697(1) c ϭ 13.874(2) A ̊] to R1 ϭ 3.6% based on 4275 reflections. These results confirm complete Si, Al ordering. Mean Si-O distances range between 1.615 and 1.629 A ̊; mean Al-O distances between 1.734 and 1.742 A ̊. Calcium is sevenfold coordinated by six framework O atoms and one H 2 O molecule. Barium is 12-fold coordinated by framework O atoms. Polarized IR spectra in the region of OH absorptions (between 5700 and 1300 cm Ϫ1 ) were recorded on polished slabs of Wasenalp armenite and structurally related milarite from Val Giuf. In general, milarite and armenite show similar anisotropy of H 2 O rel

Who reads Si, Al ordering in the double-ring silicate armenite, BaCa~2~Al~6~Si~9~O~30~.2H~2~O; a single-crystal X-ray and^29^Si MAS NMR study?

Author

Thomas Armbruster

Publisher

Mineralogical Society of America

Published

1999

Language

EN

Field

Earth and Planetary Sciences (Physical Sciences)