Whenoneendofanair-dryigneousrockblockwasuniaxiallyloadedinlaboratory,thereappearedanelectromotiveforcethatmadeelectriccurrentsflowfromthestressedvolumetotheunstressedvolume.Quartz-freerockssuchasgabbroalsogeneratedthisforce,strongerthanquartz-bearingrockssuchasgranite.Thisindicatesthatthepiezoelectriceffectofquartzandtheelectrokineticeffectofporewaterdonotmakealargecontributiontowardgeneratingtheelectromotiveforce.Wefocusonperoxybondthatisoneoftheabundantlatticedefectsinigneousrock-formingminerals.Whenmechanicalloadingdeformsthelatticestructurearoundthisdefectandbreaksitsbond,itsenergylevelschangeandactlikeanaccepter.AsanelectronistrappedatthisdefectfromaneighborO2-site,apositiveholeisactivatedthere.Theyattempttodiffusetowardtheunstressedvolumethroughthevalencebandandaresimultaneouslyaffectedbytheattractiveelectricforcewiththeelectronstrappedinperoxybonds.Thisleadstoapolarizationinthestressedvolumeandthegenerationofelectromotiveforcebetweenthestressedandunstressedvolumes.SimilarelectromotiveforcemaybegeneratedintheEarth’scrustwhereinhomogeneousstress/strainischanging.