Non destructive methodology to study GRO 95517  antarctic meteorite

INTRODUCTIONReturning sample missions have gainedincreasing attention in the last decades sincethe only way to know the planetary surface'scomposition and reconstruct the historyof geological processes is to analysesamples using Earth-ground laboratorybasedtechniques.The employment of a non-or minimally destructiveprotocol of analyses to carry out acomprehensive characterisation is crucialto preserving very precious extraterrestrialsamples.On the other hand, non-destructive analyseson samples of meteorites and micrometeoriteswere yet successfully applied on Al-Haggounia 001[1] and the micrometeoritefound on Mt. Gariglione, southern Italy[2].With this aim, we are studying a fragmentof an antarctic meteorite named GRO95517, a EH3 chondrite, found in 1995 inGrosvenor Mountains (Antarctica – NZ).The purpose of this investigation is thestudy of mineralogical composition withparticular attention to the rare phases, mineraldistribution and association, texture andmicrostructures in order to provide furtherinformation on the origin and evolution ofthis meteorite.METHODSThe fragment was studied by ScanningElectron Microscope (SEM) and microcomputedtomography (μ-CT).The correlation between SEM-EDS data,chemical mapping and 3D reconstruction byμ-CT allows to obtain us a volumetric reconstructionof the fragment in nondestructiveway.RESULTSOptical analysesGRO 95517 consists of chondrulesformed by pyroxene (enstatite) immersed ina matrix composed by mesostases of plagioclasein which nickel-iron alloys, sulfides(daubréelite, oldhamite and troilite) andphosphides (schreibersite) are disseminated.The presence of oxidised phases such asjarosite and oxides testify an heavily weathering.The sample also exhibits several fractures.Optical observations on thin sectionshow two families of enstatite chondrules(EC): radial-pyroxene chondrules consistingof fan-like arrays of enstatite and porphyriticchondrules containing mainly enstatite.Other mineralogical phases forming bothchondrules and mesostasis are mainly sulfidesand plagioclases.In one enstatite chondrule we can appreciatea “faulting” structure.Sometimes, plagioclase and quartz aggregatesare observed.SEM analysisThe S.E.M. analysis confirmed the presenceof pyroxene (enstatite), which is themain constituent of chondrules. Furthermore, a significant distributionof sulfides was detected, relativelyhomogeneously dispersed throughout thethin section. Through SEM analysis, thesesulfides are oldhamite, daubréelite, andtroilite.Significant is also the presence of ironnickelalloys (kamacite), which stand outdue to their bright white appearance in BSEimages.Secondary mineralogical phases relatedto terrestrial weathering alteration are limonite(yellowish-brown in color) and jarosite.Microcomputed Tomography (μ-CT)This non-invasive technique was crucialto obtain bulk information about the outerand inner parts of the sample, thanks to theability to provide 3D reconstruction of meteoriticfragments. GRO95517 is characterizedby a high presence of pores that, inmost cases, are filled by secondary phases. In the cross section mineralswith different attenuation coefficientsand chondrules can be observed.CONCLUSIONThe Antarctic meteorite GRO 95517 ischaracterized by primary phases such asenstatite, kamacite and troilite surroundedby a glassy mesostasis. Few secondaryphases were recognized, that indicate a highdegree of weathering (limonite and jarosite).The integration of SEM-EDS data,chemical maps and 3D μ-CT reconstructionallows to obtain a volumetric reconstructionof the fragment, providing valuable informationon its internal structure withoutcompromising its integrity.REFERENCES:[1] Manzari, P., Mele, D., Tempesta, G. &Agrosì, G. (2023) – New insights on theporosity and grain features of Al Haggounia001, an impact-melt meteorite, 1-10.[2] Agrosì, G., Manzari, P., Mele, D., Tempesta,G., Rizzo, F., Catelani, T., Cheng, G.,Yao, N., Villenueve, J. & Bindi, L. (2025) –Unique (Al, Cu)-alloys discovered in a micrometeoritefrom Southern Italy. Communicationsearth & environment, 1-10.