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 measured for an eleven-member sanidine - analbite series from room temperature to 950 degrees C. Slopes dV/dT and. in turn, coefficients of thermal expansion, vary systematically with composition, as sodic members expand to a greater degree than potassic ones, Volumes of K-Na mixing (V-ex) reach maximum values in the sodic parr of the compositional range at all temperatures, but decrease in magnitude by about 20% from room to elevated temperature, as the distribution of V-ex values also becomes increasingly symmetrical with respect to composition Transformation from triclinic to monoclinic symmetry occurs above room temperature for the five most sodic samples. Transformation temperature is related linearly to the mole fraction of potassium in the feldspar.