  We present here a methodology, using holographic interferometry, enabling to
measure the pure surface reaction rate constant of the dissolution of a mineral
in water, unambiguously free from the influence of mass transport. We use that
technique to access to this value for gypsum and we demonstrate that it was
never measured before but could be deduced a posteriori from the literature
results if hydrodynamics is taken into account with accuracy. It is found to be
much smaller than expected. This method enables to provide reliable rate
constants for the test of dissolution models and the interpretation of in situ
measurements, and gives clues to explain the inconsistency between dissolution
rates of calcite and aragonite, for instance, in the literature.
