The dissolution of forsterite and other minerals of the olivine and phenakite silicate groups are described by a novel mechanism of dissolution. For many of these minerals, the order of reaction with respect to H+ is close to0.5intheacidicregion.Themechanismofdissolutionproposedherecorrectlypredictstheseordersofreaction withoutanyadjustableparameters.Recentworkhasshownthattheorderofreactionofforsteritewithrespectto H+ changesfrom0.5intheacidicregionto0.25intheregionaboveavalueofpHofapproximately6.Previously proposed models of dissolution cannot predict this change in order of reaction, whereas the mechanism proposedheredoespredictthischangeinreactionorder,againwithoutanyadjustableparameters.Themechanism proposes that the reason for the change in order of reaction is that the H+ needs to be positioned at the inner Helmholtz plane to be effective at higher values of pH. The acceleration of the rate of dissolution by organic acidsandtheretardationoftheratebydissolvedsilicaandcarbondioxidearealsocorrectlypredicted.Themechanism predicts a change intheinterfacial potentialdifferenceatthe samevalue of pH that the order ofreaction changes.Thispredictionisverifiedbymeasurementsofthezetapotential,whichreflectsthepredictedchangein surfacepotentialatapHofapproximately6.Theproposedmechanismprovidesaframeworkfortheinterpretationofthecorrelationbetweentherateofdissolutionoftheorthosilicatesandtheexchangesratesofwaterinthe inner sphere of thecorresponding metalaqua-ion.