Thermal expansion and glass transition temperatures of synthetic glasses of plagioclase-like compositions

The glass transition temperatures and the thermal expansions both below and above the glass transition temperature region of synthetic glasses of compositions close to those of plagioclases have been determined. The linear thermal expansion coefficient of the rigid glasses decreases on average from 7.4×10^–6/dgC for albite glass to 4.9×10^–6/dgC for glass close to anorthite composition. The glass transition temperature of the glasses initially decreases from 763° C for albite glass to 752°C for An_9.7 glass and then increases nearly linearly with further increasing anorthite content to 813° C for glass close to anorthite composition.—Measurements made for comparison on a glass prepared from Madagascar orthoclase yielded a linear thermal expansion coefficient of 6.1×10^–6/dgC and a glass transition temperature of 905° C.The variations in thermal expansion and glass transition temperature of the feldspar glasses with composition are discussed in terms of structural changes which are assumed to be associated with cation replacement.