Phase E: A high pressure hydrous silicate with unique crystal chemistry

Y. Kudoh, L. W. Finger, R. M. Hazen, C. T. Prewitt, M. Kanzaki, D. R. Veblen

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Abstract

The unique cation-disordered crystal structures of two samples of phase E, a non-stoichiometric, hydrous silicate synthesized in a uniaxial, split-sphere, multi-anvil apparatus at conditions above 13 GPa and 1000° C, have been solved and refined in space group {Mathematical expression}. The compositions and unit cells for the two materials, assuming six oxygens per cell, are Mg2.08Si1.16H3.20O6, a=2.9701(1) Å, c=13.882(1) Å V = 106.05(4) Å3 for sample 1, and Mg2.17Si1.01H3.62O6, a=2.9853(6) Å, c=13.9482(7) Å, V= 107.65(4) Å3 for sample 2. The structure contains layers with many features of brucite-type units, with the layers stacked in a rhombohedral arrangement. The layers are cross linked by silicon in tetrahedral coordination and magnesium in octahedral coordination, as well as hydrogen bonds. Interlay er octahedra share edges with intralayer octahedra. Interlayer tetrahedra would share faces with intralayer octahedra. To avoid this situation, there are vacancies within the layers. There is, however, no long-range order in the occupation of these sites, as indicated by the lack of a superstructure. Selected-area electron diffraction patterns show walls of diffuse intensity similar in geometry and magnitude to those observed in short-range-ordered alloys and Hågg phases. Phase E thus appears to represent a new class of disordered silicates, which may be thermodynamically metastable.

Original languageEnglish
Pages (from-to)357-360
Number of pages4
JournalPhysics and Chemistry of Minerals
Volume19
Issue number6
DOIs
Publication statusPublished - Jan 1 1993
Externally publishedYes

ASJC Scopus subject areas

  • Materials Science(all)
  • Geochemistry and Petrology

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