Empirical Raman calibration of chlorite minerals

Abstract

Chlorite group is a common hydrated-aluminous phyllosilicate minerals found in most geological environments (e.g., hydrothermal, igneous, sedimentary, metamorphic, etc). The chemical composition of this mineral group is dependent on several conditions including temperature, pressure, and bulk rock composition. Generally, the determination of chlorite’s composition relies on electron microprobe analysis which is both timely and costly. We suggest that Raman spectroscopy as a good candidate to replace for electron microprobe analysis. This would also open up the possibly of chlorite chemical composition determination in planetary exploration. In this thesis, we demonstrate the capability of Raman spectroscopy technique to determine chemical composition of chlorite. Our results show that chlorite’s Raman peaks slightly, but quantifiably, change as a function of its chemical composition. We find that iron and magnesium composition (apfu) is linearly correlated with the peak positions of four bands. Silicon and tetrahedral aluminum are correlated with a single band’s peak position. These results allow us to propose fourteen empirical rules that will help geoscientists to quickly identify and characterize chlorite composition based on Raman spectroscopic measurements.