ORIGINALARTICLEThediscoveryofTiO2-II,thea-PbO2-structuredhigh-pressurepolymorphofrutile,intheSuizhouL6chondriteXiandeXie1•XiangpingGu2•MingChen1,3Received:27September2022/Revised:23October2022/Accepted:3November2022/Publishedonline:11December2022©TheAuthor(s),underexclusivelicencetoSciencePressandInstituteofGeochemistry,CASandSpringer-VerlagGmbHGermany,partofSpringerNature2022AbstractWereportthediscoveryofTiO2-IIintheunmeltedrockoftheshockedSuizhouL6chondrite.Nat-uralTiO2-IIwaspreviouslyfoundinultrahigh-pressuremetamorphicandmantle-derivedrocks,terrestrialimpactstructures,andtektite.Ourmicroscopic,Ramanspectro-scopic,electronmicroprobeandtransmissionelectronmicroscopicinvestigationshaverevealed:(1)AllobservedTiO2-IIgrainsarerelatedwithilmeniteandpyrophanite;(2)TiO2-IIoccursasneedle-andleaf-shapedinclusionsinilmeniteandpatch-,tape-shapedbodyinpyrophanite;(3)ThecompositionofTiO2-IIisidenticalwiththatofitsprecursorrutile;(4)TheRamanspectrumofTiO2-IIisingoodagreementwiththatofnaturalandsynthesizeda-PbO2-typeTiO2;(5)TiO2-IIoccursmainlyintheformofwell-orderednano-domainsandsmallmis-orientationamongthedomainscanbeobserved.(6)AllelectrondiffractionreflectionsfromTiO2-IIcanbeindexedtoa-PbO2structureinspacegroupPbcnwithlatticeparametersofa=4.481A�,b=5.578A�andc=4.921A�;(7)Theexsolutioninclusionsofrutilefromhostilmenitearemostlyconnectedwithanalternationprocessalongthelamellartwinningplaneofilmeniteinducedbyshock-inducedhighpressureandhightemperature;(8)TheP–Tregimeof20–25GPaand1000°CestimatedfortheSuizhouunmeltedrockissuitableforphasetransitionofrutileintoTiO2-IIphase.KeywordsRutile·TiO2-II·High-pressurepolymorph·Shockmetamorphism·Suizhoumeteorite1IntroductionRutileisacommonaccessorymineralinvarioustypesofterrestrialandextraterrestrialrocks.TiO2-IIisahigh-pressurepolymorphofrutilethatwasfirstsynthesizedbystaticcompressionexperiment(Bendelianyetal.1966)andbyshockwavetechniques(McQueenetal.1967).ThepowderX-raydiffractiondatashowthatTiO2-IIisisostructuralwitha-Pb...
