Models for the estimation of Fe³⁺/Fe_totratio in terrestrial and extraterrestrial alkali- and iron-rich silicate glasses using Raman spectroscopyk

Abstract

To develop Raman spectroscopy as a quantitative tool in both geosciences and planetary sciences the effect of iron oxidation state (Fe 3+ /Fe tot) on the Raman spectra of basaltic and pantelleritic glasses has been investigated. We have used remelted pantellerite from Pantelleria Island and synthetic ironrich basaltic glasses [from Chevrel et al. (2014)]. The Raman spectra of pantelleritic glasses reveal dramatic changes in the high wavelength region of the spectrum (800-1200 cm-1) as iron oxidation state changes. In particular the 970 cm-1 band intensity increases with increasing oxidation state of the glass (Fe 3+ /Fe tot ratio from 0.24 to 0.83). In contrast, Raman spectra of the basaltic glasses do not show the same oxidation state sensitivity (Fe 3+ /Fe tot ratio from 0.15 to 0.79). A shift, however, of the 950 cm-1 band to high wavenumber with decreasing iron oxidation state can be observed. We present here two empirical parameterizations (for silica-and alkali-rich pantelleritic glasses and for iron-rich basaltic glasses) to enable estimation of the iron oxidation state of both anhydrous and hydrous silicate glasses (up to 2.4 wt% H 2 O). The validation of the models derived from these parameterizations have been obtained using the independent characterization of these melt samples plus a series of external samples via wet chemistry. The "pantelleritic" model can be applied within SiO 2 , FeO, and alkali content ranges of ~69-75, ~7-9, and ~8-11 wt%, respectively. The "basaltic" model is valid within SiO 2 , FeO, and alkali content ranges of ~42-54, ~10-22, and ~3-6 wt%, respectively. The results of this study contribute to the expansion of the compositionally dependent database previously presented by Di Genova et al. (2015) for Raman spectra of complex silicate glasses. The applications of these models range from microanalysis of silicate glasses (e.g., melt inclusions) to handheld in situ terrestrial field investigations and studies under extreme conditions such as extraterrestrial (i.e., Mars), volcanic, and submarine environments.

Crystallization of iron‐containing sodium aluminosilicate glasses in the NaAlSiO4‐NaFeSiO4 join

“…The importance of Fe concentration to the crystalline phases formed and to the chemical durability of waste forms has been discussed in the waste glass community. However, its structural behavior in these glasses is still not well‐understood due to the complexity exerted by different redox states, as iron acts as both network former and network modifier, depending on its concentration as well as the concentration of other constituents such as Al, Si, and Na [ Di Genova et al ., ; Jantzen and Brown , , ; Jantzen et al ., ; Marcial et al ., ; Shaharyar et al ., ; Wang et al ., ; Yang et al ., ]. Therefore, understanding the role of iron in nepheline crystallization and the structure‐composition relationship would be highly beneficial, as compositions could potentially be designed to control nepheline crystallization.…”

“…In natural magmatic melts, the iron oxide concentration ranges from ~0.5 wt % in rhyolitic melts to ~20 wt % in basalts [ Kim et al ., ; Mysen and Richet , ]. It has been known that natural silicate melt properties are strongly influenced by iron content, since iron occurs in two valence states (Fe 2+ and Fe 3+ ) with different oxygen coordinations (four‐, five‐, and sixfold) which affect physical properties and crystallization of magmas [ Brearly , ; Di Genova et al ., ; Magnien et al ., , ]. Moreover, the study of Fe phase crystallization in natural glasses (e.g., obsidians, basalts, pseudotachylites, and tektites) is of great interest since the presence of fine‐grained magnetic Fe minerals, particularly magnetite, is necessary for paleomagnetism and magnetic sourcing studies.…”

Raman spectra of Martian glass analogues: A tool to approximate their chemical composition

“…Moreover, Raman spectroscopy has also been developed as a tool to investigate volcanic (calc‐alkaline) glasses and approximate their chemical composition [ Di Genova et al ., ], to estimate the iron oxidation state of iron‐rich basaltic glasses and alkali‐ and silica‐rich glasses [ Di Genova et al ., ], as well as to determine the presence of water in silicate glasses [e.g., Thomas , ; Zajacz et al ., ; Behrens et al ., ; Le Losq et al ., ].…”

“…Here we expand the compositionally dependent Raman database recently presented [ Di Genova et al ., , ] to iron‐rich basaltic and rhyolitic melts relevant to Mars. Those papers have shown how the presence of iron, and its oxidation state, greatly affects the Raman spectral features of glasses.…”

“…[] with the iron‐rich rhyolite spectrum showed in Di Genova et al . [] (sample Fsp1). As discussed in detail in Di Genova et al .…”