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Evidence for anomalously large degree of polymerization in Mg₂SiO₄ glass and melt

¹ Department of Chemical Engineering and Materials Science, University of California at Davis, Davis, California 95616, U.S.A.
² 3M Corporate Research Laboratory, St. Paul, Minnesota 55144, U.S.A.

Correspondence: ^* E-mail: sbsen{at}ucdavis.edu

Ab-initio molecular dynamics simulation of forsterite (Mg₂SiO₄) melt at 2273 K shows the presence of nearly 40% of the Si atoms as (Si₂O₇)^6– dimers. This result is directly corroborated by the ²⁹Si nuclear magnetic resonance spectrum of bulk Mg₂SiO₄ glass, prepared by containerless levitation techniques. The presence of a large excess of bridging O atoms associated with the (Si₂O₇)^6– dimers inforsterite glass and melt is in sharp contrast with their complete absence in crystalline forsterite. Such structural differences between the crystal and the melt can have important implications in understanding the dynamics of crystallization and segregation in a primordial magma ocean and the continuing chemical differentiation of the Earth.

Key Words: Ab initio molecular dynamics • forsterite • melt • glass • simulation • NMR • structure

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				G. B. Martin, F. J. Spera, M. S. Ghiorso, and D. Nevins Structure, thermodynamic, and transport properties of molten Mg2SiO4: Molecular dynamics simulations and model EOS American Mineralogist, May 1, 2009; 94(5-6): 693 - 703. [Abstract] [Full Text] [PDF]