An electron microprobe analysis, secondary ion mass spectrometry, and single-crystal X-ray diffraction study of phlogopites from Mt. Vulture, Potenza, Italy: Consideration of cation partitioning
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Ernesto Mesto
und
Luisa Ottolini
Abstract
Mt. Vulture trioctahedral micas-1M mainly consist of phlogopite-annite solid solutions with a minor component of brittle micas. However, both Li-free and Li- and F-rich compositions may coexist in the same volcano-stratigraphic level. We report the results of electron microprobe analysis (EMPA), secondary ion mass spectrometry (SIMS), and single-crystal X-ray diffraction (SCXRD) for three crystals (LC7-27Go, LC7-3Go, and LC7-1R) that are representative of both compositions.
EMPA and SIMS showed that sample LC7-1R is richer in TiO2 , Li2O, and F and poorer in H2O than the other samples.
Structure refinements using anisotropic displacement parameters for the three samples, performed in space group C2/m, converged at 3.46 ≤ R ≤ 4.34, 3.89 ≤ Rw ≤ 4.39. When considering bond distances, the three samples can be described as homo-octahedral whereas mean atomic numbers suggest that only LC7-1R is meso-octahedral. Significant differences occur among the samples for some distortion parameters commonly used for micas. In particular, LC7-1R displays higher values of BLDM2, shiftM2 and lower values of ΔK-O4 and tK-O4 than those of samples LC7-3Go and LC7-27Go. These differences are ascribed to F- and Ti-substitutions.
Cation distributions were obtained by combining EMPA, SIMS, and SCXRD data after analysis of the effect of normalization schemes commonly used in mica formula recalculation. In LC7-3Go and LC7-27Go, Ti is incorporated according to the Ti-Tschermak mechanism, whereas more than one Ti-substitution mechanism occurs in LC7-1R. For the latter sample, octahedral vacancies are present leading to a complex substitution pattern and complex structural distortions related to the special octahedral compositions that were determined.
© 2015 by Walter de Gruyter Berlin/Boston
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- Dana Lecture. Rates of Fe, Mg, Mn, and Ca diffusion in garnet
- An FTIR study of hydrogen in anorthoclase and associated melt inclusions
- First occurrence of iodine in natural sulfosalts: The case of mutnovskite, Pb2AsS3(I,Cl,Br), a new mineral from the Mutnovsky volcano, Kamchatka Peninsula, Russian Federation
- The real topological conÞ guration of the extra-framework content in alkali-poor beryl: A multi-methodological study
- A low-temperature heat-capacity study of synthetic anhydrous Mg-cordierite (Mg2Al4Si5O18)
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- Fe2+/Fe3+ charge ordering in contact layers of lamellar magnetism: Bond valence arguments
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