内蒙东乌旗石铁陨石

A Stony-Iron Meteorite Fallen to Dongujimqin, Inner Mongolia, China

１９９５年９月７日下午１时４５分在内蒙古东乌珠穆沁旗、呼热图苏木、阿日斯楞图嘎查地区（４５°２０′Ｎ，１１９°Ｅ）陨落了各相距１０ｋｍ的三块陨石，分别编号为Ｎｏ．１、Ｎｏ．２和Ｎｏ．３，其重量分别为８８．２，３８．０和２．６ｋｇ。三块陨石表面的熔壳发育程度不一，Ｎｏ．２和Ｎｏ．３熔壳发育，Ｎｏ．１不发育，表明是经历了二次爆裂破碎的结果。据肉眼观察，陨石中金属矿物和非金属矿物分布不均一，它们聚集成大小不同的团块星散分布在陨石中。Ｎｏ．２陨石有４×８ｃｍ２面积大小的辉石矿物晶体。在偏光显微镜下呈现角砾状重结晶结构，辉石和橄榄石矿物呈大小不等的角砾状颗粒，并被细小重结晶的矿物包围。铁纹石中有条带状的镍纹石，二者呈网状结构。较大的铁纹石颗粒状的中部有近球状和微小粒状的陨硫铁矿物。陨石的矿物组成中，金属矿物以铁纹石为主，其次为镍纹石和陨硫铁等。非金属矿物以辉石（Ｆｓ＝２４．７９，Ｗｏ＝２．９１，Ｅｕ＝７２．３０）为主，其次有橄榄石（Ｆｏ＝６２，Ｆａ＝３５）、斜长石（Ａｎ＝８９．５，Ａｂ＝１０，Ｏｒ＝０．５）、鳞石英、磷镁钙矿、磷钙石和堇青石等。陨石化学成分分析表明，金属含量为５０．６７（％），非金属为４１．７６（％）?

A meteorite shower fell at 13:45′ on September 7, 1995, at the area of Arisilengtugacha 150km to the southeast of the town of Dongujimqin, Inner Mongolia, China, i.e. 45°30′N, 119°E. Three fragments of 88.2kg(No.1), 38.0kg(No.2) and 2.6kg(No.3) were recovered from a narrow area about 20 km long in the direction of north south. From the appearances, all of three neteorites have fusion crusts in varying degrees. The meteorite samples of No.2 and No.3 have more well-developed fusion crusts than the No.1 has. It implies that the No.1 may has experienced disruption. By the observation on surfaces of the meteorites although there are pyroxene fragments with diameters about 4 to 8 cm, which were scattered in the meteorites, most of metallic minerals (50.67%) and non-metallic minerals (41.76wt%) were finely disseminated and were inhomogeneously distributed. Among the metallic minerals the main component is kamacite and others are taenite, troilite and schreibersite. For non metallic minerals the dominant mineral is pyroxene (Fs=24.79, Wo=2.91, Eu=73.30), some other minerals include plagioclase(An=89.5, Ab=10, Or=0.5), olivine (Fo=62,Fa=38), tridymite, stanfieldite, whitlockite and cordierite. Pyroxene is brecciform surrounded by numerous fine grained crystals. Also the grains of olivine and plagioclase are irregular. Whithin the grain of kamacite there are banded taenite, and both of them constitute a net like texture. Some fine grained troilite crystals and fine grained prismatic schreibersite crystals occurs in kamacite. According to the analyses of mineral constituents and textures, the Dongujimqin Meteorites can be identified as mesosiderite of stony iron meteorites.