Magnetic and metallographical studies of the Bocaiuva iron meteorite

The Bocaiuva iron meteorite (IAB) has been studied magnetically and metallographically in order to understand its stable natural remanent magnetization (NRM). This meteorite consists of a large amount of 6-7wt% Ni kamacite, associated with taenite, plessite, schreibersite and magnetite. Tetrataenite less than 0.2% in volume occurs along the high-Ni taenite lamellae and in the kamacite domain walls beside its lamellae. The NRM direction is almost parallel to a dominant plane of tetrataenite development. The Bocaiuva may have acquired the NRM in the slow cooling process under 300℃ of the meteorite\u27s parent body or after shock heating by collisions

Observation of Allende and Antarctic meteorites by monochromatic X-ray CT based on synchrotron radiation

Three-dimensional CT images of the Allende meteorite with a high resolution of 10μm have been obtained nondestructively by a monochromatic X-ray computed tomography (CT) based on synchrotron radiation (SR). The metallic minerals, matrix and chondrules can be clearly observed in the CT images. The CT values, which express the image intensity, allow a quantitative elemental analysis including such as difference in the metallic minerals, i. e., pentlandite and troilite, using the comparison of CT images and elemental images measured by a computer-aided microanalyzer (CMA). The three-dimensional CT images indicate that the metallic minerals surround some chondrules, and the largest chondrule has two humps and well crystallized olivine in its center. These observations suggest that the three-dimensional SR-CT system is a useful method for identification of internal structures of stony meteorites. Additionally, information obtained from the CT images of Antarctic meteorites confirms that the SR-CT system can be applied to classification of stony chondrites

Magnetic analyses of new Antarctic iron meteorites

Four new Antarctic iron meteorites collected at Yamato meteorite ice field in 1979,Yamato-790517,-790724,-791076 and -791694,are magnetically analyzed. Characteristics of their magnetic hysteresis curves and thermomagnetic curves indicate the following meteoritic structures of these iron meteorites. Yamato-790517 is a Ni-poor ataxite consisting of kamacite matrix of 6.4 wt% Ni, unequilibrated Ni-rich kamacite specks of about 12 wt% Ni and taenite specks. Yamato-790724 is a coarse octahedrite of kamacite matrix of 7.0 wt% Ni and taenite specks. yamato-791076 is a finest octahedrite or an ataxite which consists of kamacite of 7.3 wt% Ni and plessite of about 12 wt% Ni. Yamato-791694 is a Ni-rich ataxite consisting mostly of taenite of about 40 wt% Ni and a small amount of kamacite specks. Two Antarctic iron meteorites collected near Allan Hills in Victoria Land in 1977,Allan Hills-77263 and -77289,also are magnetically analyzed. Both the iron meteorites are coarse octahedrites comprising kamacite matrix of about 6.5 wt% Ni and taenite specks

Chemical studies on the Antarctic iron meteorites, Yamato-790724, ALH-77263 and ALH-77289

Three Antarctic iron meteorites, Yamato-790724,ALH-77263 and ALH-77289 have been studied from the viewpoint of analytical chemistry. Fourteen elements, Ni, Co, P, As, Au, Cr, Ga, Ge, Ir, Pt, Re, Ru, Sb and W were determined. From the results, Yamato-790724 was classified into Group IIIA. ALH-77236 and ALH-77289 were classified into Group I. The elemental distributions of Ni, Co, P and S in the three meteorites were examined. Phosphide, (Fe, Ni)_3P and sulphides, FeS and FeCr_2S_4,were detected. Morphology of the compounds was observed and the distribution of them was measured. Some discussions are given to the facet pits formed by the etching method and the orientations. Twinned structures found in ALH-77289 are considered to have been caused by strong mechanical shock

Chemical studies on the distribution of germanium and gallium in Antarctic iron meteorites

Three Antarctic iron meteorites, Yamato-790517,Y-791076 and Y-791694,were analyzed and Y-790517 was classified as a IIIA meteorite. Elemental distributions of Ge, Ga, P, S, Co and Ni in the six Antarctic iron meteorites, ALH-77263,ALH-77289,Y-790724 and the three meteorites listed above, were examined and mapped by a newly developed computer-aided microanalyzer (CMA) and presented in color printouts