Abstract
Water can form different chemical bonds with the ionic entities composing silicate melts. Because of that, its influence on the physico-chemical properties of magmas can vary with silicate composition and water content, temperature, and pressure. To further our understanding of how silicate chemical composition governs proton distribution in magmas, the environment of protons in hydrous alkali (Li, Na, K) silicate glasses was varied as a function of the type of alkali metal and total water content. From 1H MAS NMR spectroscopy, H+ are distributed among five different structural environments in alkali silicate glasses. One of these environments is in the form of H2O molecules (H2Omol). The four others are the proton environments associated with Si-OH bonding, and perhaps also with M-OH bonding (with M = Li, Na, or K). Those environments differ in their O-O distance and extent of hydrogen bonding. H2Omol species are located in an environment with an O-O distance of ~290 pm. OH- groups are in environments with O-O distances from 240 to 305 pm. The ionic radius of the alkalis, and hence their ionic field strength, determines the fraction of water dissolved as H2Omol and OH- groups, as well as the distribution of protons in the various OH- environments. The mean volume of the H+ oxygen coordination sphere was calculated using the 1H+ NMR signal intensity and the mean O-O distance around H+. Increasing ionic radius of the alkali metal in silicate glasses results in a decrease of this mean volume. The partial molar volume of water in the corresponding melts determined through other technics seems to vary in a comparable way. Therefore, the chemical composition of silicate melts may control the partial molar volume of dissolved water because of its influence on the structural environment of protons. This probably also plays a role in determining water solubility.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Anhydrite: An important sulfur binder limiting the climatic impact of subaerial volcanic eruptions
- Tweed, twins, and holes
- The chemical behavior of fluids released during deep subduction based on fluid inclusions
- In situ observation of the pyroxene-majorite transition in Na2MgSi5O12 using synchrotron radiation and Raman spectroscopy of Na-majorite
- Prevalence of growth twins among anhedral plagioclase microlites
- Intrinsic conditions of magma genesis at the Lunar Crater Volcanic Field (Nevada), and implications for internal plumbing and magma ascent
- A rock fragment related to the magnesian suite in lunar meteorite Allan Hills (ALHA) 81005
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- Kojonenite, a new palladium tin telluride mineral from the Stillwater Layered Igneous Intrusion, Montana, U.S.A.
- Cathodoluminescence dependence on feldspar mineral structure and implications for forensic geology
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- Alkali influence on the water speciation and the environment of protons in silicate glasses revealed by 1H MAS NMR spectroscopy
- Carbonate mineralization in percolated olivine aggregates: Linking effects of crystallographic orientation and fluid flow
- The catalytic effect of bound extracellular polymeric substances excreted by anaerobic microorganisms on Ca-Mg carbonate precipitation: Implications for the “dolomite problem”
- Experimental study along the magnesio-hornblende–glaucophane join
- Direct observation of Ca-Na ordering and structure polarity in Ca-rich intermediate plagioclase feldspar with incommensurate modulated structure
- Stability and adhesion of calcite/montmorillonite assembly
- Experimental and modeled chlorine solubilities in aluminosilicate melts at 1 to 7000 bars and 700 to 1250 °C: Applications to magmas of Augustine Volcano, Alaska
- Cation order-disorder in Fe-bearing pyrope and grossular garnets: A 27Al and 29Si MAS NMR and 57Fe Mössbauer spectroscopy study
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- Klebelsbergite, Sb4O4SO4(OH)2: Stability relationships, formation in Nature, and refinement of its structure
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- New Mineral Names
- Book Review
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