2018/02/08 by Danilo Bersani, Irene Aliatis, Mario Tribaudino +8 · 2 citations
Earth and Planetary Sciences · #Geological and Geochemical Analysis #High-pressure geophysics and materials #Mineralogy and Gemology Studies
paper · doi:10.1002/jrs.5340
openalex publication_date 2018/02/08 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/29
Abstract Plagioclase undergoes complex exsolution and ordering and phase transition processes during their evolution in nature, and this has hindered attempts to define simple trends relating the major peaks of their Raman spectra with composition. Here, the peak position and linewidth of major Raman features have been calibrated for a set of 20 plagioclases, spanning from albite to anorthite in composition, with symmetry and ordering states that were already well characterized. Point group symmetry is the most important factor determining the Raman peak behaviour with composition, though C , I , and P plagioclases show different trends for the position of the main peak ν a at ~500 cm −1 . Using a simplifying approach, which merges the effect of Al–Si ordering and incommensurate modulations, a method has been developed to estimate the plagioclase composition from calibration of a few determinative Raman peaks. This makes use of the wavenumber difference Δ ab between the most intense peaks ν a and ν b around 500 cm −1 , the linewidth Г a of the strongest ν a peak, and the wavenumber difference Δ cb between ν c and ν b peaks, where ν c is a Raman feature at ~560–580 cm −1 . The calibration was completed from data sets composed of spectra from metamorphic to pegmatitic plagioclase. The results were then tested against a further data set, mostly made by volcanic plagioclase. In most samples, the difference between electron micro probe analysis (EMPA) and Raman compositions is less than 5%. Higher residuals (beyond 10%) are observed for intermediate plagioclase, suggesting that some differences in Δ ab exist between volcanic and metamorphic plagioclase of intermediate compositions. The Raman compositional results for a plagioclase from Marsili submarine volcano agree with composition and zoning found from the analysis by laser ablation.