Synthesis of K₂SiSi₃O₉ with silicon in 4- and 6-coordination

Abstract

Summary Two kinds of vitreous material with composition K 2 GeSi 3 O 9 and K 2 Si 4 O 9 were treated under conditions of high temperature and pressure. The X-ray diffraction patterns of the products were similar to that of K 2 TiSi 3 O 9 , which has the wadeite, K 2 ZrSi 3 O 9 , 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 K 2 Si 4 O 9 . Since Zr ions in wadeite are in a 6-coordinated site, one-quarter of Si ions in K 2 Si 4 O 9 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.