We found a match
Your institution may have access to this item. Find your institution then sign in to continue.
- Title
Optimal Raman-scattering signal for estimating the Fe3+ content on the clinozoisite–epidote join.
- Authors
Nagashima, Mariko; Mihailova, Boriana
- Abstract
To provide a tool for fast estimation of the Fe 3+ content in Ca 2 (Al, Fe 3+)3 Si 3 O 12 (OH) epidote grains, including in thin sections and crude-rock samples, we applied Raman spectroscopy to 33 areas from 15 natural samples with Fe 3+ ranging from 0.22 to 1.13 atoms per formula unit (apfu), the chemistry of which was independently determined by wavelength-dispersive electron microprobe analysis (WD-EPMA). The Raman spectra were collected from the very areas subjected to WD-EPMA. We have analysed both the OH-stretching region (3215–3615 cm -1) and the spectral range generated by the framework vibrations (15–1215 cm -1). Similarly to the IR spectra, the Raman peaks in the OH-stretching region shift toward higher wavenumbers with increasing Fe. However, the quantification of Fe 3+ based on OH-stretching Raman peaks can be hindered by the multicomponent overlapping and significant intensity variations with the crystal orientation. Among the Raman signals generated by framework vibrations, the position of four peaks (near 250, 570, 600, and 1090 cm -1) exhibit a steady linear regression with the increase in Fe content (in apfu). However, the peak near 250 cm -1 attributed to MO 6 vibrations also depends on the crystal orientation and therefore is not always well resolved, which worsens the accuracy in Fe-content determination based on its position. The peaks near 570, 600, and 1090 cm -1 arise from Si 2 O 7 vibrational modes, and although their intensities also vary with the crystal orientation, all three signals are well resolved in a random orientation. However, among the three Si 2 O 7 -related signals, the 570 cm -1 peak is the sharpest (peak width <10 cm -1) and is easily recognized as a separate peak. Hence, we propose to use the position of this peak as a highly reliable parameter to estimate the Fe content, via the linear trend given as ω570=577.1(3)-12.7(4)x , where ω is the wavenumber (cm -1) and x is Fe content (apfu), with accuracy ± 0.04 Fe 3+ apfu. The peaks near 600 and 1090 cm -1 may be complementarily used for the Fe estimate, based on the following relations: ω600=611.6(2)-13.8(4)x and ω1090=1098.8(3)-13.5(5)x. Analyses of the effect of Sr as a substitution for Ca and Cr at the octahedral sites indicate that contents of Sr <0.12 apfu do not interfere with the quantification of Fe via the ω570 (x) relation, whereas Cr >0.16 apfu leads to overestimation of Fe; Cr presence can be recognized however by the broadening of the peaks near 95 and 250 cm -1.
- Subjects
ELECTRON probe microanalysis; CRYSTAL orientation; SERS spectroscopy; SIGNALS &; signaling; EPIDOTE; RAMAN spectroscopy
- Publication
European Journal of Minerology, 2023, Vol 35, Issue 2, p267
- ISSN
0935-1221
- Publication type
Article
- DOI
10.5194/ejm-35-267-2023