Journal Article

Vibrational and structural insight into silicate minerals by mid-infrared absorption and emission spectroscopies

Zhu, Ying, Zhang, Yuanlong, Lu, Anhuai, Li, Yan, Ding, Hongrui, Wang, Changqiu, Ji, Xiang, Li, Yanzhang

2022

Overview

Silicate minerals are essential bricks of solid planets, which have been studied deeply by infrared absorption spectroscopy. Along with the rapid development of planetary exploration, infrared emission spectroscopy and corresponding radiation properties of minerals have been receiving attention. However, systematic research on silicate minerals using infrared emission spectroscopy has been absent so far. In this work, various silicate minerals (totally ten in five series included nesosilicates, eyclosilicates, inosilicates, phyllosilicates and tectosilicates) were investigated infrared spectral characteristics and infrared radiation properties using X-ray diffraction, X-ray fluorescence, and infrared spectroscopy (absorption and emission spectroscopy). Results indicated that the assignment of each band in infrared emission spectra of all samples could be obtainable referring to the well-known infrared absorption spectra, presenting a dominant absorption band near 1000 cm −1 related with the stretching of Si–O bonds and several weak bending-driven absorption bands in the range of 400–650 cm −1 . A good linear relationship (coefficient of determination R 2  = 0.996) between two corresponding wavenumbers suggested emission bands of silicate minerals have great correspondence with their absorption bands. Both vibrational stretching and bending of Si–O bonds in both spectra regularly shifted to higher frequencies as the increase of Si/O from 0.25 for nesosilicates and 0.50 for tectosilicates. The average emissivity of silicates, obtained from radiation energy spectra from 400 to 2000 cm −1 in the temperature range of 50–140 °C, showed all silicate minerals presented relatively higher emissivity (> 0.910) and displayed a remarkable reduction from nesosilicates (e.g., 0.981 for forsterite) to tectosilicates minerals (e.g., 0.913 for quartz). It was thus concluded that higher emissivity of silicates was attributed to the decrease of polymerization degree of SiO 4 tetrahedron ( R 2  = 0.86), vibrational frequency and range for Si–O stretching ( R 2  = 0.88, 0.92, respectively), and vibrational range for Si–O bending ( R 2  = 0.85). This work gets insight into the relationship among spectral characteristics, crystal chemistry, and radiation properties of silicate minerals, and would help accurately identify and distinguish various silicate minerals in remote sensing analysis for understanding the composition of planetary surfaces and their evolutionary path.

• Publisher: Springer Berlin Heidelberg,Springer Nature B.V
• Subject: Absorption spectra / Absorption spectroscopy / Bending / Bonding strength / Crystallography and Scattering Methods / Earth and Environmental Science / Earth Sciences / Emission spectra / Emission spectroscopy / Emissivity / Energy spectra / Forsterite / Geochemistry / Infrared absorption / Infrared astronomy / Infrared radiation / Infrared spectra / Infrared spectroscopy / Mineral exploration / Mineral Resources / Mineralogy / Minerals / Original Paper / Planetary composition / Planetary surfaces / Remote sensing / Silica / Silicates / Silicon / Space exploration / Stretching / Tetrahedra / X-ray diffraction / X-ray fluorescence