Xieite,a new mineral,occurs in the shock vein of the Suizhou meteorite.The mineral has an ortho-rhombic structure and its space group is Bbmm.The cell parameters are a = 9.462(6),b = 9.562(9),c = 2.916(1).The crystal-chemical formula is(Fe0.87Mg0.13Mn0.01)1.01(Cr1.62Al0.25Ti0.08V0.02)1.97O4,or simply formula FeCr2O4.Stronger X-ray diffraction lines are [d(),I/Io]:(2.675,100),(2.389,20),(2.089,10),(1.953,90),(1.566,60),(1.439,15),(1.425,15),(1.337,40).Xieite is a high pressure polymorph of FeCr2O4 and formed by solid-state transformation of chromite under shock-induced high pressure and tem-perature,in association with other high-pressure minerals including ringwoodite,majorite,lingunite and tuite.The P-T condition for the formation of xieite is estimated to be 18―23 GPa and 1800―1950℃,respectively.Xieite has recently been approved by the Commission on New Minerals,Nomenclature and Classification of the International Mineralogical Association(IMA 2007-056).The mineral name,xieite,is named after Xiande Xie.
The synchrotron radiation X-ray diffraction technique developed for in situ study ahigh pressure and temperature has also been used to investigate microscopic mineral inclusionsin ultrahigh-pressure metamorphic rocks and deep-mantle samples. Present study added twomore examples of successful utilization of synchrotron radiation X-ray diffraction technique for insitu investigations of fine-grained (0.5―30 μm in size) minerals in very thin shock melt veins othe Suizhou meteorite: ( i ) X-ray diffraction measurement of extremely small-sized vein matrixminerals, and (ii) identification of the micron-sized new mineral tuite embedded in the vein matrixIt has been revealed that the fine-grained vein matrix consists of well crystallized garnet, kamacite and troilite, and the powder diffraction pattern consisting of 17 lines with d-values, intensities( I ), relative intensities (I/Io) and Miller indices, as well as the cell parameters for the new mineratuite has also been successfully obtained. The result of present investigations has enriched thecontent of dynamic high-pressure mineralogy and that of Earth’s mantle geochemistry.
XIE Xiande1, SHU Jinfu2 & CHEN Ming1 1. Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
