Raman Spectroscopy of Analog Minerals of Relevance to Lunar and Planetary Exploration

Abstract:

The present study focuses on the Raman spectroscopy of an assortment of Mars and lunar analog mineral samples, namely olivine, plagioclase (anorthite, bytownite, labradorite), pyroxene (augite), ilmenite, and apatite. The ability to distinguish compositional variations in these minerals on a planetary body is key to establishing environmental conditions and geologic history. Minerals in lunar basalts and regolith, such as ilmenite and pyroxene, are known hosts of metals like Cr, Ni, Co, and Mn, and ilmenite in particular has been considered for Fe and oxygen extraction, which is critical for resource identification and for developing a viable long-term lunar exploration program. In order to better understand the nature of the fundamental vibrations of analog minerals, we have performed an in-depth analysis of the major vibrational features associated with the Raman spectra for each sample using a visible (VIS) excitation laser (at 514 nm) and a near IR (NIR) excitation laser (at 780 nm). Basalt and ilmenite samples were better characterized under NIR excitation, while the silicate minerals had a better response under VIS excitation. We also investigated the effect of temperature on the vibrations for a select group of mineral samples over a temperature range 300 – 473 K under NIR excitation. Our results showed an enhancement of spectral peak intensity for minerals like plagioclase as the temperature increased up to 373K, but a decrease at temperatures beyond that.

*Acknowledgments: P. Misra and R. Coleman, Jr. acknowledge support from NASA (Award # 80NCCS20M019 & NNX17AJ48G); P. Misra, M. Peterson and M. Howard acknowledge financial support from NSF (Award # PHY-1659224); and D. Bower would like to acknowledge the support of the Internal Research and Development and Fundamental Laboratory Research Programs at Goddard Space Flight Center.