K₂Si₄O₉: energetics and vibrational spectra of glass, sheet silicate, and wadeite-type phases.

Calorimetric experiments were performed on three phases of K₂Si₄O₉: a high-P phase with the wadeite structure containing both tetrahedrally and octahedrally coordinated Si, a low-P phase with a complex sheet structure containing solely tetrahedrally coordinated Si, and glass. Newly measured IR and Raman spectra of each phase are presented. -J.A.Z.