Precise determination of Mg/Fe ratios applicable to terrestrial olivine samples using Raman spectroscopy

The relationship between Mg# [ = 100 Mg/(Mg + Fe) in mol] and the Raman shift was analyzed precisely for olivine [(Mg, Fe)2SiO4] samples with Mg# between 100 and 62.8. Two prominent peaks at 826820 cm-1 (peak 1) and 858849 cm-1 (peak 2) and three subordinate peaks at 883881 cm-1 (peak 3), 920914 cm-1 (peak 4), and 967951 cm-1 (peak 5) were observed to shift monotonously to lower wavenumbers with decreasing Mg#. The ?Mg#( = Mg#ref - Mg#) versus ??(= ?ref - ?) can be linearly regressed for each peak as ?Mg# = A ??, where ? is a peak wavenumber of olivine with Mg# ranging from 100 to 62.8, and ?ref is that of olivine with a reference value of Mg#, namely, Mg#ref. We set Mg#ref as 100 (i.e.pure forsterite Mg2SiO4) whereas A is a regression parameter (5.789, 4.294, 12.34, 6.348, and 2.09, respectively,for peaks 1, 2, 3, 4, and 5). This equation enables us to avoid small inter-laboratory differences of wavenumber calibration. The equation for peak 2 yields estimations of Mg# in geologically satisfactory precision, +/- 1 Mg# (1s) in the Mg# range of 10062.8. Copyright (C) 2011 John Wiley & Sons, Ltd.