Synthesis and structure of a stuffed derivative of α-quartz, Mg0.5AlSiO4

Hongwu Xu, Peter J. Heaney, Ping Yu, Huifang Xu

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8 Scopus citations

Abstract

A structural derivative of quartz with the composition Mg0.5AlSiO4 has been grown from glass and characterized using synchrotron X-ray diffraction (XRD), transmission electron microscopy (TEM), and 29Si nuclear magnetic resonance (NMR) spectroscopy. Rietveld analysis of the XRD data indicates that the framework of Mg0.5AlSiO4 is isostructural with a-quartz, rather than b-quartz, as is consistent with previous theoretical modeling (Sternitzke and Müller 1991). Al and Si exhibit long-range disorder over the framework tetrahedral sites, indicated by the absence of the superlattice reflections corresponding to the doubling of c relative to that of quartz. Nevertheless, 29Si NMR measurements show that Al and Si exhibit partial short-range order with an ordering degree of 56%. Electron diffraction reveals superlattice reflections indicative of doubled periodicities along the a-axes. Fourier electron density maps show that Mg occupies channel sites that each are bonded to six O atoms, in contrast to the tetrahedral coordination of Li in the β-quartz-type framework for β-eucryptite, LiAlSiO4. Furthermore, the concentrations of Mg in adjacent channels are different, resulting in framework distortions that generate the superstructures along a.

Original languageEnglish (US)
Pages (from-to)2191-2198
Number of pages8
JournalAmerican Mineralogist
Volume100
Issue number10
DOIs
StatePublished - Oct 1 2015

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology

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