AtmosphericEnvironment38(2004)3617–3624 DistributionchangesofMn 2+ andFe 3+ onweatheredmarble surfacesmeasuredbyEPRspectroscopy KyriakiPolikreti*,YannisManiatis Laboratory of Archaeometry, Institute of Materials Science, N.C.S.R. ‘‘Demokritos’’, Aghia Paraskevi Attikis 153 10, Greece Received4August2003;receivedinrevisedform25February2004;accepted15March2004 Abstract The behavior of Mn 2+ andFe 3+ on weathered marble surfaces was studied by electron paramagnetic resonance spectroscopy(EPR).ThepaperisconcentratedinMn 2+ andFe 3+ replacingCa 2+ intheCaCO 3 ofmarble.Nineteen marblesamplesofdifferenttypesandexposedtodifferentenvironmentalconditionswereanalyzed:Samplesofvarious grainsizesandmanganeseconcentrations,samplesfromquarryfronts,excavationsandmonumentsexposedinruralor pollutedenvironments. Mn 2+ doesnotshowasystematicbehaviorbutFe 3+ decreasesupto100%onthesurface,comparedtothemarble bulk.Thedepletionstartsatadeptharound4mmfromtheoutersurface.Thephenomenonisexplainedbydissolution andre-crystallizationofcalcitetogetherwithmicrobe-mediatedreductionofFe 3+ toFe 2+ .Higherdecreaseisobserved on samples of low-grade metamorphosis, on excavated samples and samples exposed to heavily polluted urban environment. Unexpectedly,thisdepletionextendsdeeperthantheactualweatheringdepth(measuredbySEM),i.e.thedecreasein Fe 3+ concentrationextendsbeyondthepatina–marbleinterface,uptoafewmillimetersintothehealthymarble.This additionaldepletionmaybeexplainedbysolid-statediffusionofiron.Suchahypothesishasalreadybeenreportedin literatureforotherionsincalcitecrystals. r 2004ElsevierLtd.Allrightsreserved. Keywords: Marble;Weathering;EPRspectroscopy;Iondistribution;Iron;Manganese 1. Introduction The majority of studies on marble weathering use total concentrations of trace elements to describe ionic balance on marble surfaces, i.e. concentrations of ions in the CaCO 3 lattice together with ions in impurities, diagenetic or contaminants (Del Monte et al., 1987; Margolis and Showers, 1988; Ulens et al., 1995; Moropoulou et al. 1998; Polikreti and Maniatis, 2003). This macroscopic approach results in useful, practical weathering models but leaves the actual alterations induced in ‘‘healthy’’ marble lattices poorly understood. Thepresentworkaimstorevealandunderstandthe ionic changes induced in the crystal lattice of marble surface layers, in atomic scale and estimate the contribution of these changes to weathering rates and finalconditionofthecrystallinematerial.Thetechnique of electron paramagnetic resonance spectroscopy is idealforthispurpose,duetoitscapabilitytodistinguish ions in different environmental symmetries and record their concentration changes in various weathering conditions. EPR spectroscopy has been used for 15 yearsinourlaboratory,onmarblecharacterizationand provenanceinvestigation(PolikretiandManiatis,2002), ARTICLE IN PRESS *Correspondingauthor. E-mail address: kpolikre@ucy.ac.cy(K.Polikreti). 1352-2310/$-seefrontmatter r 2004ElsevierLtd.Allrightsreserved. doi:10.1016/j.atmosenv.2004.03.048