Raman spectral features of a natural chromitite from NW Türkiye: Characterization of magnesiochromite spectra and implications

Abstract

In this work, a first detailed Raman spectroscopic measurement study of natural magnesiochromites from a multi-textural ophiolitic chromitite sample from Harmancık district in north-western Türkiye has been presented to characterize the Raman spectral features of Turkish high-Cr ophiolitic chromitites. The magnesiochromites in the multi-textural chromitite sample has an almost uniform composition, with Cr2O3, Al2O3, and TiO2 contents being 62.02 wt%, 9.18 wt%, and 0.14 wt% in average, respectively. Cr#s are 0.82 and Mg#s are 0.65 in average, in the ranges that of typical ophiolitic chromitites of boninitic to arc-related affinity. Despite this uniform composition, three distinctive Raman spectra morphologies (Types I, II and III) are determined. Of these, the Type I spectra is by far the dominant. Three common main band clusters are defined (BG- 1, BG-II and BG-III) for all of the morphological types. The BG-I (~385-605 cm-1) and BG-II (~649-739 cm-1) are the main clusters that incorporate the high intensity and descriptive peaks and shoulders. The BG-III includes the very low intensity broad bands around 1122 to 1763 cm-1, considered as overtones of the BG-I, and BG-II. Four of the several bands in the BG-I and BG-II has been assigned to the A1g (~690 cm-1), F2g(3) (~605 cm-1), F2g(2) (~555 cm-1), and Eg (~470 cm-1) modes of spinel. Of the several un-assigned bands, the ~730 cm-1 band has been interpreted to be related with the high-Cr nature of the studied sample. The variance in this band’s intensity has been interpreted to be related with concomitant or post-crystallization textural arrangement and the plastic mantle deformation. This result emphasize the viability of a preliminary approach on orientation of the magnesiochromites in the ophiolitic chromitites via Raman spectroscopy, if the composition variable can be constrained.