Abstract
A new high-pressure form of topaz-OH (denoted here topaz-OH II) was obtained at 14 GPa and 1400 °C. The X-ray diffraction patternof this phase can be indexed by an orthorhombic cell with a = 4.72318(5), b = 8.91480(9), and c = 2.77276(3) Å. The lengths of a andb are similar, but c is approximately a third of that for a previously reported topaz-OH (denoted topaz-OH I). The structural formula of topaz-OH II can be written as (Al 0.68Si0.32(O0.66(OH)0.34) 2, suggesting significant cation disorder in the structure. The crystal structure of topaz-OH II is solved using powder synchrotron X-ray diffraction data, and refined with constraints provided by a separate multi-nuclear NMR study. The structure has similarities with topaz-OH I and diaspore (α-AlOOH) structures, having partially occupied double edge-shared octahedral chains, and 2 × 1 tunnels with partially occupied tetrahedral and octahedral sites.
Original language | English |
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Pages (from-to) | 1349-1352 |
Number of pages | 4 |
Journal | American Mineralogist |
Volume | 95 |
Issue number | 8-9 |
DOIs | |
Publication status | Published - 2010 |
Keywords
- Crystal structure
- High-pressure studies
- Order-disorder
- Phase transition
ASJC Scopus subject areas
- Geophysics
- Geochemistry and Petrology