Petrology And Mineralogy Of Primitive Ordinary Chondrite NWA 13171

NWA 13171 meteorite is a newly discovered primitive ordinary chondrite that has not experienced obvious thermal metamorphism.In this work,the petrological and mineralogical characteristics of the meteorite were studied by means of scanning electron microscope（SEM）electron probe and laser Raman.The results are as follows:1)NWA 13171 meteorite has typical characteristics of ordinary chondrite.The abundance of each component in the meteorite is:chondrules 76.8 vol%;matrix12.5 vol%;metal and opaque minerals（troilite,kamacite,taenite）10.7 vol%.2)Chondrules quantity and type is rich,clear boundary and formed a circle-nearly round oval or fragmented and has obvious olivine component band,the average diameter of 0.74 mm.The chondrules types are:porphyritic olivine and pyroxene chondrule（47.5 vol%）;porphyritic olivine chondrule（26.2 vol%）;porphyritic pyroxene chondrule（18.3 vol%）;bar shaped olivine chondrule（3 vol%）;radial pyroxene chondrule（1 vol%）;cryptocrystalline chondrule（3.4 vol%）and glass chondrule（0.7 vol%）.3)All silicate minerals have a small impact fracture surface;The phenomenon of wave extinction can be seen in olivine under orthogonal polariscope.No impingement fusion capsule and impingement fusion vein were found in meteorite.4)There is a weak oxidation edge around the metal and sulfide,and the meteorite as a whole has a small oxidation vein.According to statistics,about 50%of the iron and nickel metal and meteorite sulfide oxidize,and some silicate minerals are infected by oxides.5)The composition of silicate minerals showed strong heterogeneity:olivine Fa _{14.9（0.8-30.7）}（PMD=87.5）,low calcium pyroxene Fs _{12.4（1.7-34.7）}（PMD=81.2）,the average content of Cr2O3 in iron peridotite was 0.2 wt%,standard deviation=0.1.6)The metal minerals are mainly iron and nickel alloy,with a wide range of components.The electron probe profile analysis of iron and nickel alloy particles shows that iron and nickel alloy particles have typical“M”type band characteristics.7)The organic matter（OM）in the meteorite matrix is black fine-grained porous particles.Raman spectrogram data of the organic matter shows that the half-peak width of peak D（FWHM-D）is 144.2 ^cm-1 on average.According to the above NWA 13171 meteorite petrology and mineralogical characteristics,the following main conclusions are drawn:1)NWA 13171 is a primitive chondrite type L 3.1.2)NWA 13171 has an shock degree of S2 and weathering degree of W2.3)the parent asteroid of NWA 13171 underwent a very slow cooling history after its formation,with a cooling rate of about 0.1/Myr.