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Although it has been well accepted that F-Al linkages dominate in F-bearing alkali aluminosilicate glasses, the possibility of F-Si linkages remains unresolved. Recent 19F NMR results have been interpreted as indicative of not only the presence of the Al-F-Na(n) linkages but also of the presence of Si-F-Na(n) linkages. High level ab initio NMR calculations were performed to investigate the nature of possible species contributing to the 19F spectra. (more…)

Ab initio, molecular orbital calculations were carried out to study the energetic stability and NMR characteristics of “triclusters” of composition [T(XO)(OH)2]O[Al(OH)3][T(OH)3] (X = no atom, H+, Li+, Na+, K+, Mg2+, or Ca2+; T = Si4+ or Al3+). These triclusters consist of a central oxygen atom in trigonal coordination (IIIO) surrounded by three tetrahedrally coordinated, network-forming cations (Al and Si). All tricluster configurations modeled are predicted to be dynamically stable except for one containing three Al3+ cations. Tricluster viability was further tested by computing energetic stabilities relative to Al(OH)3 and dimers with non-bridging oxygen atoms (NBO). With these species as reactants and T = Si4+, calculated reaction energies vary from –87 kJ/mol with X = H+, to –253 kJ/mol with X = Mg2+. For the case of X = Ca2+, where structures with 1 Si and 2 Al were also modeled, the reaction energy was found to be over 50 kJ/mol more negative in the latter case (–278 kJ/mol compared to –222 kJ/mol). (more…)

Dissolved H2O, CO2, S and Cl concentrations were measured in glasses from Tanzilla Mountain, a 500 m-high, exposed subglacial volcano from the Tuya-Teslin region, north central British Columbia, Canada. The absence of a flat-topped subaerial lava cap and the dominance of pillows and pillow breccias imply that the Tanzilla Mountain volcanic edifice did not reach a subaerial eruptive phase. Lavas are dominantly tholeiitic basalt with minor amounts of alkalic basalt erupted at the summit and near the base. Tholeiites have roughly constant H2O (c.0.56 ± 0.07 wt%), CO2 (<30 ppm), S (980 ± 30 ppm) and Cl (200 ± 20 ppm) concentrations. Alkalic basalts have higher and more variable volatile concentrations that decrease with increasing elevation (0.62–0.92 wt% H2O, <30 ppm CO2, 870–1110 ppm S and 280–410 ppm Cl) consistent with eruptive degassing. Calculated vapour saturation pressures for the alkalic basalts are 36 to 81 bars corresponding to ice thicknesses of 400 to 900 m. (more…)

Despite the importance of the chloride ion in magmas and the fluids that separate from them, very little is known about atomic-scale structural environments for Cl– in silicate glasses. We present here the first solid-state 35Cl NMR data for Cl in silicate and aluminosilicate glasses, made possible by the availability of very high (14.1 to 18.8 Tesla) magnetic fields. (more…)

We have determined infrared molar absorptivities for water absorption bands in Fe-bearing and Fe-free andesitic glasses. Water dissolves in andesitic glasses as both hydroxyl groups and molecular water as observed in other silicate glasses. Concentrations of molecular water and hydroxyl species are a strong function of total water content. IR molar absorptivities for Fe-bearing andesite are 3570 = 62.32 ± 0.42 L/mol·cm, 4500 = 0.79 ± 0.07 L/mol·cm, (more…)

Small-scale analyses of volatiles in minerals and glasses provide information on how volatiles influence high-temperature geologic processes and low-temperature alteration processes. Four techniques for determining the C-O-H volatile contents of andesitic glasses are compared: manometry, secondary ion mass spectrometry, micro-Fourier transform infrared spectroscopy, and a technique where the H2O content is calculated using the difference between electron microprobe analysis totals and 100% sum. We present a method to determine the H content of a wide range of glass and mineral compositions using secondary ion mass spectrometry and a model for calibration factors. (more…)

Submarine pillow basalts (34 Ma) recovered from the Northern Kerguelen Plateau at ODP Site 1140 contain abundant unaltered glass, providing the first opportunity to measure the volatile contents of tholeiitic basaltic magmas related to the Kerguelen mantle plume. The glasses have La/Sm and Nb/Zr ratios that vary from values similar to Southeast Indian Ridge (SEIR) MORB (Unit 1), to slightly more enriched (Unit 6), to values transitional between SEIR MORB and basaltic magmas formed by melting of the Kerguelen plume (Units 2 and 3). Volatile contents for glasses in Units 1 and 6 are similar to depleted mid-ocean ridge basalt (MORB) values (0·25–0·27 wt % H2O, 1240–1450 ppm S, 42–54 ppm Cl). (more…)

1 Dipartimento di Scienze della Terra, Università di Messina, Salita Sperone 31, I–98166 S. Agata di Messina, Italy
2 Istituto Nazionale per la Fisica della Materia and Dipartimento di Fisica, Università di Bologna, viale Berti Pichat 6/2, I–40127 Bologna, Italy
3 European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble, France

* Corresponding author, e-mail: simonaq@unimo.it

The X-ray Absorption Near Edge Structure technique has been successfully applied to the study of ancient glasses from Patti Roman Villa (Messina, Sicily). (more…)

The composition of glasses used in glass-ionomer cements affects their leaching behavior and hence the properties of the cement. The aim of this study was to correlate the composition and leaching behavior of these glasses with their infrared absorption characteristics. The wavenumber of the absorption band of the Si-O asymmetric stretching vibration AS shifts to a higher value with decreasing content of mono- and bivalent cations in the glass. (more…)