A wide range of natural K-, Na-, Ca-or (K + Li)-micas have been systematically examined by Raman spectrometry. The spectra are interpretable in terms of regular variations in peak positions and chemical parameters. Several vibrations give higher wavenumbers for Na-micas compared to K-micas, in accord with the smaller ionic size of Na + than K +. The =195 cm -1 and ~270 cm -1 peak wavenumbers and intensities vary as functions of the chemistry of the octahedral sites, i.e. the replacement of Mg 2+ by Mn 2+, Zn 2+, Cr 3+, Fe 3+, Ti 4+ , and especially by AP +, or by a vacancy, and the replacement of (OH)-by F-. The group of ~700 cm -1 peaks vary in wavenumber and intensity with the replacement of Si by A1 in the tetrahedra; distinct Si-O-Si and Si-O-AI vibrations can be recognized. Di-and tri-octahedral micas are distinguished on the basis of certain relative peak intensities which vary considerably with polarization direction, and of trends with increasing Al (iv), A1 (vi) or A1 (t~ Calibration of these trends for the chemical analysis of mica microinclusions seems feasible once the uncertainties in the data set are resolved by the determination of further samples selected to highlight the effect of specific elements.
Abstract. Raman microprobe spectra were made on three post shock, diaplectic plagioclase feldspars. Optical and Xray diffraction studies indicated that feldspars maintained a partially or totally crystalline state after having passed through the mixed phase zone of Hugoniot response to shock waves (15-38 GPa). The appearance of uniquely glass-type spectra occurs at different shock pressures for each specimen according to its atomic structural arrangement, below 38 GPa for mosaic structured labradorite, near 40 GPa for anorthite and above 50 GPa for the highly ordered low albite. The diaplectic anorthite and labradorite glasses give spectra which indicate the presence of two glass types. Shifts in the band envelope frequencies compared to spectra of fused glass and statically pressure densified glass suggest that these glasses have specific structural arrangements. These differences suggest that the shock and fusion glass-forming processes are not exactly identical.The results from material shocked in the mixed phase region of Hugoniot response show that the phase transitions are effected at different pressures depending upon the feldspar structural type.
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