title: Silicon coordination and speciation changes in a silicate liquid at high pressures.
abstract: Coordination and local geometry around Si cations in silicate liquids are of primary importance in controlling the chemical and physical properties of magmas. Pressure-induced changes from fourfold to sixfold coordination of Si in silicate glass samples quenched from liquids has been detected with (29)Si magic-angle spinning nuclear magnetic resonance spectrometry. Samples of Na(2)Si(2)O(5) glass quenched from 8 gigapascals and 1500 degrees C contained about 1.5 percent octahedral Si, which was demonstrably part of a homogeneous, amorphous phase. The dominant tetrahedral Si speciation in these glasses became disproportionated to a more random distribution of bridging and nonbridging oxygens with increasing pressure.
authors.forename: X
authors.initials: X
authors.lastname: Xue
authors.forename: M
authors.initials: M
authors.lastname: Kanzaki
authors.forename: R G
authors.initials: RG
authors.lastname: Trønnes
authors.forename: J F
authors.initials: JF
authors.lastname: Stebbins