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

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.