The Crystal Chemistry of Rhodizite: A Re-Examination

A. Pring1, *, V. K. Din2, D. A. Jefferson1 and J. M. Thomas1
1 Department of Physical Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EP
2 Department of Mineralogy, British Museum (Natural History), Cromwell Road, London SW7 5BD
*Present address: South Australian Museum, North Terrace, Adelaide, South Australia, 5000.

Abstract: The crystal chemistry of rhodizite was re-examined using data from high-resolution electron microscopy (HREM), magic angle spinning nuclear magnetic resonance (MASNMR), a single crystal X-ray structure refinement, and a new chemical analysis. The analysis calculates to the formula: (K0.46Cs0.36Rb0.06 Na0.02)Σ0.90Al3.99Be4(B11·35Be0.55Li0.02)O28· The distribution of alkali cations was shown to be truly random by HREM images and computer image simulations. The distribution of boron and beryllium was monitored by MASNMR, the spectra for both elements gave only single resonances indicating that all beryllium and boron atoms are located in chemically equivalent sites. The structure of rhodizite was refined by single crystal X-ray diffraction techniques. The mineral is cubic a = 7.318(1) Å, space group P4¯3m. A full matrix least-squares refinement using 152 unique observed reflections [F > 3σ(F)] converged to R = 0.0344. The refinement confirmed the basic structure as determined by Taxer and Buerger (1967), 4 beryllium atoms of the unit cell were found to occupy a 4e special position, the remaining 0.5 being randomly distributed with the 11.35 boron atoms over the 12h sites.

Keywords: rhodizite • crystal chemistry • high-resolution electron microscopy • magic angle spinning nuclear magnetic resonance

Mineralogical Magazine; March 1986 v. 50; no. 355; p. 163-172; DOI: 10.1180/minmag.1986.050.355.22
© 1986, The Mineralogical Society
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