Empirical Raman calibration of trioctahedral ferromagnesium chlorite minerals

Abstract

Chlorite is a common hydrated‐aluminous phyllosilicate mineral group that forms in most geological environments (e.g., hydrothermal, igneous, sedimentary, and metamorphic). The chemical composition of chlorite depends on several factors including temperature, pressure, fluid, and bulk rock composition. Raman spectroscopy is proposed as a quick and cost‐effective alternative to scanning electron microscopy and electron probe micro‐analysis, which involve complex sample preparation. In this paper, we demonstrate that Raman spectroscopy is a viable technique to determine the chemical composition of chlorite. Our results show that chlorite's Raman spectra changes quantitatively as a function of its chemical composition. Iron (Fe) and magnesium (Mg) content (APFU) is linearly correlated with the peak positions of three bands: Band 1 (99–104 cm−1), Band 8 (546–553 cm−1), and Band D (3,570–3,580 cm−1). In contrast, silicon (Si) and tetrahedral aluminum (AlIV) are correlated with a single band's position, Band 9b (663–679 cm−1). We derived 18 empirical rules from these correlations, aiding geoscientists in accurately identifying and determining chlorite composition using Raman spectroscopy. Moreover, this technique holds potential for determining chlorite's chemical composition during planetary exploration, leveraging existing Raman spectrometers deployed on Mars and for future space missions.