Mineralogical and Petrographical Studies of the Yamato Meteorites, Yamato-7301(j), -7305(k), -7308(l) and -7303(m) from Antarctica

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In 1973,the 14th Japanese Antarctic Research Expedition party collected twelve meteoritic stones in the bare ice field near the Yamato Mountains, Antarctica. Four of the stones were named Yamato-7301,-7305,-7308 and -7303. Yamato-7301,-7305 and -7303 are ordinary chondrites and are classified respectively as H4,L5 and L5 chondrites, while Yamato-7308 is a howardite. Yamato-7301,-7305 and -7303 are composed chiefly of olivine ((Fo)_<75-80>) and orthopyroxene ((En)_<75-83>), with subordinate amounts of clinopyroxene, plagioclase and phosphate minerals. Opaque minerals, nickel-iron, troilite and chromite, are more abundant in Yamato-7301 than in Yamato-7305 and -7303. Yamato-7308 is composed mainly of pyroxene and plagioclase (anorthite), with olivine, silica minerals, opaque minerals and glassy material in minor amounts. The composition of orthopyroxene is variable ranging from (En)_<80> to (En)_<37>, and also clinopyroxene varies considerably in composition. The result suggests that Yamato-7308 originated from the fractional crystallization of the parent magma of the achondrite.
国立極地研究所の論文