Structural Characteristics of Liquid Mixtures of Feldspar and Silica

Abstract

Thermodynamic properties of liquid mixtures of feldspar and silica were considered in attempting to interpret them in terms of melt structure. Two sources of data were used: the heats of formation and free energies of formation of the crystalline and glassy compounds, and the published phase diagrams. The systems albite‐silica, orthoclase‐silica, and anorthite‐silica were studied, and some data from the system celsian‐silica were included. A model which assumes a random distribution of AlO 4 tetrahedra and SiO 4 , tetrahedra is generally applicable to silica‐rich liquid mixtures of albite‐silica and orthoclase‐silica. For mixtures of albite‐silica, it is suggested that minor amounts of polymeric aluminosilicate units are also present. In liquid mixtures of anorthite and silica, however, it is necessary to assume that polymeric units like 4AlO 2 .3SiO 2 or 4AlO 2 .2SiO 2 , are the dominating feature of the structure.