Alkali feldspar unit-cell parameteras at liquid nitrogen temperature: Low temperature limits of the displacive transformation

Unit-cell parameters of analbite, low albite, high sanidine, maximum microcline, and adularia have been determined at room and liquid nitrogen temperatures. In all feldspars b and ß are unchanged in this temperature interval, while a undergoes significant contraction. Interaxial angles show little change in low albite, maximum microcline, and high sanidine, though analbite displays a significant increase in α and γ (and thus an increase in obliquity) with decreasing temperature. An increase in γ of adularia from 90.00° to 90.07° may indicate a low-temperature displacive transformation from a monoclinic to a triclinic phase.