On the shape of Fe-Ni grains among ordinary chondrites
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概要
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The irregular shape and anisotropic orientation of Fe-Ni grains are quantitatively described in eight ordinary chondrites from Antarctica. The chondrites studied include three H types : ALH-77233 (H4), ALH-77182 (H5) and ALH-77115 (H6); four L types : Y-74191 (L3), ALH-77230 (L4), ALH-77254 (L5) and ALH-78105 (L6) and one LL type : Y-75258 (LL6). The axial ratio (b/a), where a and b are the longest and semi-major axial lengths respectively, the area (S), and the circumferencial length (l) with appropriate divider opening (d) are measured for each Fe-Ni grain. The orientation distribution of the longest axis indicates that L chondrites are more anisotropic than H chondrites, though the number of grains is limited. The shape parameter defined by l/√<S> is used as a quantitative indicator for the shape irregularity of Fe-Ni grains. Though the value of the shape parameter depends on d, it increases with the area for each chondrite with a fixed d of 0.01 mm. The fractal dimension is estimated by -(log N)/(log d), where N is the number of segments for circumferencial length and d is varied from 0.01 mm to 0.15 mm. The fractal dimensions thus obtained for several grains in H4,H6,L4 and L6 chondrites are all about 1.4 and do not appreciably differ from each other. It means that the irregularity of the shape of Fe-Ni grains is self-similar in the range of d used. The average value of the shape parameter (S.P.) for each sample is defined as l/(n×ΣS)^<1/2>, and appears to decrease with the increase of petrologic types from 4 to 6 for both H and L chondrites. The value of S.P. and the volume fraction of Fe-Ni grains correspond more or less well with the strength represented by the vibrational fracturing rate measurements (FUJII et al., Mem. Natl Inst. Polar Res., Spec. Issue, 20,362,1981).
- 国立極地研究所の論文
著者
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Ito Keisuke
Department Of Earth Sciences Faculty Of Science Kobe University
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Miyamoto Masamichi
Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo
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Fujii Naoyuki
Department of Earth Sciences, Faculty of Science, Kobe University
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Kobayashi Yoji
Department of Earth Sciences, Faculty of Science, Kobe University
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Kobayashi Yoji
Department Of Earth Sciences Faculty Of Science Kobe University
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Fujii Naoyuki
Department Of Earth Sciences Faculty Of Science Kobe University
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Ito Keisuke
Department Of Applied Biological Chemistry Graduate School Of Agricultural And Life Sciences The Uni
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Miyamoto Masamichi
Department Of Earth And Planetary Science Graduate School Of Science University Of Tokyo
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