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STRUCTURAL INVESTIGATIONS OF NATURAL AND SYNTHETIC CHLORITE MINERALS BY X-RAY DIFFRACTION, MÖSSBAUER SPECTROSCOPY AND SOLID-STATE NUCLEAR MAGNETIC RESONANCE

Åsa Zazzi¹, Tomas K. Hirsch^2,, Ekaterina Leonova², Andrei Kaikkonen², Jekabs Grins³, Hans Annersten⁴ and Mattias Edén^2,*

¹ Department of Chemistry, Royal Institute of Technology, SE-100 44 Stockholm, Sweden
² Physical Chemistry Division, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden
³ Inorganic Chemistry Division, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden
⁴ Department of Earth Sciences, Uppsala University, SE-752 36 Uppsala, Sweden

^* E-mail address of corresponding author: mattias{at}physc.su.se

The structures of one synthetic and two natural chlorites of the chlinochlore type were explored using X-ray diffraction, magic-angle spinning nuclear magnetic resonance (NMR) and Mössbauer spectroscopy. Rietveld refinements indicated that all structures are of the trioctahedral ordered IIb polytype. Mössbauer spectra provided the ratio ^IIFe/^IIIFe but gave no evidence for the presence of ^IIIFe in the brucite-like sheet. We also report unit-cell parameters, Mössbauer isomeric shifts, ²⁹Si NMR chemical shifts as well as ²⁷Al isotropic shifts and quadrupolar coupling parameters. Very broad ²⁹Si NMR peaks from the natural samples prevented us from obtaining accurate information on the Si-Al ordering in the tetrahedral sheets; the limitations of ²⁹Si NMR as applied to natural chlorites are discussed. High-resolution 3QMAS NMR resolved the ²⁷Al signal of the M4 octahedral site in the brucite-like sheet from the other three Al signals of crystallographically inequivalent octahedral positions.

Key Words: ²⁷Al NMR • Cation Distributions • Chlorite • Layered Mineral • Mineral Structure • Mössbauer Spectroscopy • ²⁹Si NMR • XRD

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