Understanding the Raman spectral features of phyllosilicates

Phyllosilicates, one of the five major structural types of silicates, have highly variable structures and very complex chemistry. This manuscript reports the first comprehensive Raman spectroscopic study of the five major groups of phyllosilicates. We first demonstrate that phyllosilicates have a unique Raman spectral pattern that can be used to distinguish them from orthosilicate, chain silicate, ring silicate, and framework silicate with different degrees of silicate polymerization. Second, we distinguish characteristics of Raman spectral features associated with phyllosilicates of the different stacking sequences and show how minor changes in chemical compositions and structural details in some phyllosilicates can affect their Raman spectral patterns, peak positions, and peak widths. From this study, we extract several empirical rules that can help to identify and characterize phyllosilicates based on in situ Raman spectroscopic measurements. These results are significant for planetary surface exploration, especially Mars, where the existence of phyllosilicates as a result of alteration of primary minerals has been indicated by Vis-Near IR spectroscopy used in orbital remote sensing and recently by X-ray diffraction in surface exploration. The spectral data collected from this study are also useful for laboratory study of terrestrial phyllosilicate samples. Copyright © 2015 John Wiley & Sons, Ltd.