Summary: Two kinds of vitreous material with composition K₂GeSi₃O₉ and K₂Si₄O₉ were treated under conditions of high temperature and pressure. The X-ray diffraction patterns of the products were similar to that of K₂TiSi₃O₉, which has the wadeite, K₂ZrSi₃O₉, structure.

A natural crystal of K-feldspar was also treated under the same conditions. The product was found to consist of three phases, coesite, kyanite, and the above-mentioned K₂Si₄O₉. Since Zr ions in wadeite are in a 6-coordinated site, one-quarter of Si ions in K₂Si₄O₉ are considered to be in 6-coordination. This is the first silicate in which Si ions occupy sites of 4- and 6-coordinations in one crystal at the same time.