Gneiss-distilledwaterinteractionatroomtemperaturewasinvestigatedwithbatch-reactorstostudywater-rockreactionandgeochemicalevolutionoftheaqueousphasewithtime.Theionconcentrationsinwaterwerecontrollednotonlybythedissolutionofprimaryminerals,butalsobytheprecipitationofsecondaryminerals.Thedecreasingfractionsizesofgneisscouldfavordissolutionandprecipitationsimultaneously.Ca2+andK+werethemajorcations,andHCO3-wasthemajoranioninwater.AlltheionsexceptCa2+increasedinconcentrationwithtime.TheCa2+releasefromtherocktotheaqueousphasewasinitiallymuchfasterthanthereleaseofK+,Na+andMg2+.Butafterabout5-24hours,theCa2+concentrationsinwaterdecreasedveryslowlywithtimeandbecamerelativelystable.Duringtheexperiment,thewatervariedfromtheCa-(K)-HCO3-typewatertotheK-Ca-HCO3-typewater,andthentotheK(Ca,Na)-HCO3-typewater.Thewater-gneissinteractionwasdominatedbythedissolutionofKfeldsparinthesolution.Theremainingsecondarymineralsweremainlykaolinite,illiteandK(Mg)-mica.
