  We have performed holographic interferometry measurements of the dissolution
of the (010) plane of a cleaved gypsum single crystal in pure water. These
experiments have provided the value of the dissolution rate constant k of
gypsum in water and the value of the interdiffusion coefficient D of its
aqueous species in water. D is 1.0 x 10^-9 m2 s^-1, a value close to the
theoretical value generally used in dissolution studies. k is 4 x 10^-5 mol
m^-2 s^-1. It directly characterizes the microscopic transfer rate at the
solid-liquid interface, and is not an averaged value deduced from quantities
measured far from the surface as in macroscopic dissolution experiments. It is
found to be two times lower than the value obtained from macroscopic
experiments.
