Abstract
High-resolution 29Si and 27Al NMR techniques have been applied to resolve the Si-Al distribution and coordination in the high-pressure CaAl4Si2O11 (CAS) phase, a potentially important mineral in subducted crustal materials in the deep mantle that has a unique hexagonal ferrite structure containing two octahedral (M1; M2) and one trigonal bipyramidal sites. The 29Si MAS NMR spectra of the CAS phase synthesized at 20 GPa and 1400~1600°C show two broad, asymmetric peaks near -92.7 and -182.7 ppm with an intensity ratio of 1:3, suggesting that 1/4 of the Si are in tetrahedral coordination and 3/4 in octahedral coordination. Therefore, the trigonal bipyramidal and M1 octahedral sites are each occupied by equal proportions of Si and Al, and the former are effectively half-occupied face-sharing tetrahedra (at least for Si). The 27Al MAS and 3Q MAS NMR spectra contain only one unresolved peak typical of octahedral Al with a range of quadrupolar coupling constants
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Review Paper. Microbe-clay mineral interactions
- Chemical substitutions, paragenetic relations, and physical conditions of formation of högbomite in the Sittampundi layered anorthosite complex, South India
- Miguelromeroite, the Mn analogue of sainfeldite, and redefinition of villyaellenite as an ordered intermediate in the sainfeldite-miguelromeroite series
- Mechanism and kinetics of a mineral transformation under hydrothermal conditions: Calaverite to metallic gold
- A statistical reassessment of the evidence for the racemic distribution of quartz enantiomorphs
- On the crystal structure and crystal chemistry of pollucite, (Cs,Na)16Al16Si32O96·nH2O: A natural microporous material of interest in nuclear technology
- The effect of fluid inclusion size on determination of homogenization temperature and density of liquid-rich aqueous inclusions
- Effect of SiO2, total FeO, Fe3+/Fe2+, and alkali elements in basaltic glasses on mid-infrared
- Influence of cation size on the low-temperature heat capacity of alkaline earth metasilicate glasses
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- Geochemistry of reversible hydratable tephra from the Trans Mexican Volcanic Belt
- Physical contradictions and remedies using simple polythermal equations of state
- Thermodynamic and crystallographic properties of kornelite [Fe2(SO4)3·~7.75H2O] and paracoquimbite [Fe2(SO4)3·9H2O]
- Humidity-induced phase transitions of ferric sulfate minerals studied by in situ and ex situ X-ray diffraction
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- New insights into smectite illitization: A zoned K-bentonite revisited
- The hydrothermal conversion of kaolinite to kalsilite: Influence of time, temperature, and pH
- Sideronatrite, Na2Fe(SO4)2(OH)·3H2O: Crystal structure of the orthorhombic polytype and OD character analysis
- Anharmonic OH vibrations in brucite: Small pressure-induced redshift in the range 0–22 GPa
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- Letter. Crystal structure of argentopyrite, AgFe2S3, and its relationship with cubanite
- Letter. Magnetite-free, yellow lizardite serpentinization of olivine websterite, Canyon Mountain complex, N.E. Oregon
- Letter. The influence of atomic size and charge of dissolved species on the diffusivity and viscosity of silicate melts
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