Synthetic Mn-Kilchoanite—a new development in polymorphism of melilite

Abstract

AbstractTwo compounds with the chemical composition Ca2.32Mn0.68Si2.00O7 were synthesized from a molten carbonating silicate with the melilite composition. The synthetic samples were subsequently characterized by X-ray powder diffraction, IR absorption and EPMA, and they proved to be the anhydrous phases isomorphous with kilchoanite Ca3Si2O7 and åkermanite Ca2MgSi2O7 respectively, and to be polymorphous with each other. Their crystallochemical properties suggest that Mn-åkermanite is a high-temperature structure type of Mn-kilchoanite. Substitution of Mn2+ with an intermediate ionic radius between those of Mg2+ and Ca2+ cations establishes the polymorphic relationship between åkermanite Ca2MgSi2O7 and kilchoanite Ca3Si2O7.