Characterizing amorphous silicates in extraterrestrial materials: Polymerization effects on Raman and mid‐IR spectral features of alkali and alkali earth silicate glasses

Abstract

Amorphous silicates are common in extraterrestrial materials, especially in carbonaceous chondrites of petrologic types 1 and 2. In addition, high percentage of amorphous components and poorly crystalline phyllosilicates were found in the mudstones at Gale Crater by the CheMin instruments on board of Mar Curiosity rover, which illustrates the importance of characterizing amorphous silicates in future planetary surface explorations. The structure of an amorphous silicate can vary in two aspects: the degree of polymerization and the degree of crystallinity. Here we present the first phase study on characterizing synthetic alkali and alkali earth silicate glasses with different degrees of polymerization by using vibration spectroscopy. Compared with crystalline silicates, their Raman and mid‐IR spectra show broad spectral peaks but have the similar peak positions. We find that a change in the degree of polymerization of these silicate glasses affects their Raman band positions, especially the ratio of Raman band intensities, as well as the positions of the Christiansen feature and reststrahlen bands in their mid‐IR absorbance spectra. Based on these observations, we establish a calibration curve that could enable semiquantification of the polymerization degree of silicate glasses in planetary surface/subsurface materials during future robotic planetary surface exploration missions.

Retrieving magma composition from TIR spectra: implications for terrestrial planets investigations

“…We are able to refer at this emissivity maximum caused by Christiansen effect as the Christiansen Feature (hereon CF, also present in literature as Christiansen maximum) 3,36 . Other works focusing on emissivity and or reflectance of silicates have individuated CF as a useful spectral feature 37–39 , and it is particularly efficient when glasses are taken into account, because of the scarcity of spectral features in amorphous materials 10,40,41 .…”

“…Although glasses lack long-range order, short or medium range order are present as a structural feature in the overall chaotic geometrical arrangement of the elements, allowing us to use vibrational spectroscopy on glasses 46 . Interpretation of the IR spectra from glasses has been proposed in literature 40,41 mainly concerning synthetic simple compositions related to earth as well as terrestrial planets 17–29 .…”

“…Similarly, six samples were synthesized by mixing the basalt:rhyolite of the Snake River Plain compositions in the following ratios: 100:0, 80:20, 60:40, 40:60, 20:80 and 0:100 (here named B, B8, B6, B4, B2, RB). For the spectral analysis, glasses were crushed and sieved down to <25 µ m. This grain size limit provides good contrast in the spectral response when working in the mid-IR range 40,58 .…”

Discerning Lunar Pyroclastic and Impact Glasses via Raman Spectroscopy

“…For silicate glasses, the ratio of nonbridging oxygen per tetrahedrally coordinated cations (NBO/T) is a parameter to characterize the degree of polymerization of structure (Fu et al., 2017; Mysen & Richet, 2005; Prata et al., 2019). For examples, a three‐dimensionally interconnected structure has NBO/T = 0, a chain or single ring has NBO/T = 2, and so on (Mysen & Richet, 2005).…”

Alkali Activation of Copper and Nickel Slag Composite Cementitious Materials

“…The low Raman shift range is the complex mixed stretching and bending vibration of the Si-O bridging -Si. This mode is the reticular [SiO 4 ] 4− tetrahedral structure [27].…”