Vitreous forsterite (Mg2SiO4): Synthesis, structure, and thermochemistry

Here we report the first synthesis of a forsterite (Mg2SiO4) composition gl ass as an essentially phase-pure bulk material. Under containerless conditi ons, with heterogeneous nucleation sites minimized, glass forms by cooling ca. 1 mm liquid Mg2SiO4 droplets in oxygen at 700 K/s. Si-29 NMR spectrosco pic data indicate that the SiO4 tetrahedra and MgO6 octahedra exist in a co rner sharing arrangement in the glass, but upon crystallization the polyhed ral units reorganize to form edge-sharing linkages. Transposed temperature drop calorimetry shows that the glass is 61.4 +/- 1.3 kJ/mol higher in enth alpy than the crystal.