Silicon Coordination and Speciation Changes in a Silicate Liquid at High Pressures

• DOI: 10.1126/science.245.4921.962
• Publication Date: 2006-10-05T21:21:28Z
• Authors: Xianyu Xue; Masami Kanzaki; Reidar G. Trønnes; Jonathan F. Stebbins
• Keywords: 0301 basic medicine; 03 medical and health sciences; 0103 physical sciences; 01 natural sciences

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°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.