Raman spectroscopy is used to identify the sulfur speciation (sulfur valence state) in “technical” iron-free soda-lime and potassium-silicate glasses and in “natural” glass compositions such as basalt, andesite, and rhyodacite. The presence of sulfate (S6+) is marked in Raman spectra of oxidized synthetic and natural glasses by bands at ~990 and ~1000 cm−1, respectively. The presence of sulfide (S2−) in the reduced technical glasses is marked in Raman spectra by a band at 2574 cm−1 indicating that S2− is present as HS in these Fe-free glasses. Such a band is absent in the Raman spectra of reduced basaltic, andesitic, and rhyodacitic glasses. However, an additional band at ~400 cm−1 appears in the Raman spectra of the reduced S-bearing “natural” glasses when compared to that of S-free reduced “natural” reference glasses indicating that S2− is most likely complexed with Fe in these glasses. Thus, the dissolution mechanism of S2− appears to be different in Fe-free and Fe-bearing glasses and S2− is dissolved as either HS-species or Fe-S complexes, respectively. The data shown here demonstrate the potential of Raman spectroscopy in identifying the sulfur valence state in silicate glasses. In addition, S2− is dissolved as completely different complexes when comparing “technical” iron-free and “natural” iron-bearing, hydrous silicate glass compositions.

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