Inter-diffusion of K and Na in alkali feldspar was studied at 5 and 15 kbar confining pressure
using diffusion couples annealed at 900° and 1000° C. Concentration profiles were
measured using an electron microprobe and results were obtained for inter-diffusion in four
crystallographic directions at 1000° C. Inter-diffusion coefficients (D) were calculated as a
function of composition from Or10 to Or80. Alkali inter-diffusion is about 10 times faster
normal to (001) than normal to (010), and the rate is intermediate parallel to [100] and [011] …

The rates of homogenization of coherent exsolution lamellae in cryptoperthites have been
used to evaluate K-Na interdiffusion in alkali feldspars. An “average” interdiffusion coefficient
(D) is between 2 and 4 x 10-17 cm2/sec for a synthetic cryptoperthite at 600° C in the
composition range Or23-Or53, and between 6 and 12 x 10-16 cm2/sec for a natural
cryptoperthite at 650° C in the composition range Or0-Or85. These values are for diffusion
normal to (8 01) at 1 atmosphere pressure. K-Na interdiffusion coefficients calculated from …