We haveinvestigatedthenanotextureandcrystallographicorientationofaragoniteinacoralskeleton using synchrotron-basedscanningtransmissionX-raymicroscopy(STXM)andtransmissionelectron microscopy(TEM).Polarization-dependentSTXMimagingat40-nmspatialresolutionwasusedto obtain anorientationmapofthe c-axis ofaragoniteonafocusedionbeammilledultrathinsectionofa Porites coral. Thisimagingshowedthatoneofthebasicunitsofcoralskeletons,referredtoasthecenter of calcification(COC),consistsofaclusterof100-nmaragoniteglobulescrystallographicallyaligned over severalmicrometerswithafan-likedistributionandwiththepropertiesofsinglecrystalsatthe mesoscale.Theremainderoftheskeletonconsistsofaragonitesingle-crystalfibersincrystallographic continuitywiththenanoglobulescomprisingtheCOC.Ourobservationprovidesinformationonthe nm-scaleprocessesthatledtobiomineralformationinthissample.Importantly,thepresentstudy illustrateshowthemethodologydescribedhere,whichcombinesHRTEMandpolarization-dependent synchrotron-basedSTXMimaging,offersaninterestingnewapproachforinvestigatingbiomineralizing systems atthenm-scale.