High-temperature X-ray investigation of sanidine-analbite crystalline solutions; thermal expansion, phase transitions, and volumes of mixing

Unit-cell parameters and volumes have been determined for an 11-member sanidine-analbite series from room T to 950 degrees C. Slopes of dV/dT and coefficients of thermal expansion vary systematically with composition, with sodic members showing greater expansion than potassic ones. Volumes of K-Na mixing reach maximum values in the sodic range at all T, but decrease in magnitude by approximately 20% from room to elevated T. Transformation from triclinic to monoclinic symmetry occurs above room-T for the five most sodic samples. Transformation T is related linearly to the mole fraction of K in the feldspar.