  Alkali diffusion is a first-order control for microstructure and
compositional evolution of feldspar during cooling from high temperatures of
primary magmatic or metamorphic crystallization, and knowledge of the
respective diffusion coefficients is crucial for reconstructing thermal
histories. Our understanding of alkali diffusion in feldspar is, however,
hindered by an insufficient grasp of the underlying diffusion mechanisms. We
performed molecular dynamics simulations of sodium feldspar (Albite) containing
different point defects using a recently developed neural network potential. A
high degree of agreement between the sodium self-diffusion coefficients
obtained from model simulations and those determined experimentally in earlier
studies motivated a detailed investigation into the interstitial and vacancy
mechanisms, corresponding jump rates, correlation factors and anisotropy. We
identified a dumbbell shaped double occupancy of an alkali site as an important
point defect and a correlation effect originating from the orientation of the
dumbbell as a possible cause for the $\perp\!\!(001) > \, \perp\!\!(010)$
diffusion anisotropy, which has been reported in a slew of feldspar cation
diffusion experiments.
