Crystal Structures Of Several Typical Meteorite Mineral Phases

NWA5508 meteorites are CV3 class carbonaceous chondrites.Meteorites contain a large number of chondrules,refractory inclusions and creep olivine aggregates.Jeminay meteorite is an octahedral iron meteorite,which contains inclusions and nickel-rich zone.However,there is no detailed record in the international meteorite database about NWA5508 and Jeminay.In the present work,the crystal structures of mineral phases of monocrystalline particles in NWA5508 meteorite and jeminay meteorite were studied by utilizing four-circle single crystal X-ray diffractometer.The phase identification and microstructure analysis were also carried out by means of scanning electron microscope?SEM?,transmission electron microscope?TEM?and Raman spectroscopy.Firstly,the element distribution of the chondrules,olivine and vermicular olivine aggregate contained in NWA5508 meteorites has been studied by SEM.Combined with ICP fluorescence analysis,its contained mineral phases were determined to be olivine,enstatite,meteorite sulphide,feldspar,meteorite phosphoferrite,magnetite and josephinite.The crystal structure models of a new discovered phase of Fe₃Ni₅ has been established based on the crystal structure of Rh₅V₃?Pmma?.Meanwhile,the mechanical stability,thermodynamic stability and dynamic stability of different Fe₃Ni₅ models have been simulated by first-principles method.Secondly,the observation of metallographic structure shows that the Jeminay meteorite has a very regular and orderly widmanstatten striation structure.The crystal structure of kamacite and taenite has been analyzed by powder XRD and TEM.The formation condition and parent information of kamacite were analyzed by the bandwidth of kamacite and the changing rule of elements.The experimental results show that nickel on grain stone cross section nickel element behaves a M-type rule changes with a cooling rate between 50²000?/Ma.The main components of the inclusions in the Jeminay meteorite are olivine,and a small amount of chromite.Compounds with chemical composition of Fe_83.63Co_2.43Ni_13.883.88 and Fe_83.79Co_2.19Ni_14.044.04 were found outside the widmanstatten tectonic region.Finally,the crystal structures of the olivine inclusions of NWA5508 meteorite and Jeminay meteorite has been analyzed by means of four-cricle single crystal X-ray diffractometer.In the NWA5508 meteorite sample,the chemical formula of the olivine phase is determined to be Mg_1.99Fe_0.01SiO₄.Two kinds of olivine single crystal have been determined with chemical formulae of(Mg_0.75,Fe_0.25)₂SiO₄ and(Mg_0.76,Fe_0.24)₂SiO₄.According to the atomic distribution in the olivine phases,it was found that with the increasing of element iron,the number co-occupied iron and magnesium atoms also increases and resulting a high iron/magnesium ratio,correspondingly.