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Yamato 790727
Basic information Name: Yamato 790727
     This is an OFFICIAL meteorite name.
Abbreviation: Y-790727
Observed fall: No
Year found: 1979
Country: Antarctica [Collected by National Institute of Polar Research, Japan]
Mass:help 120.4 g
NHM Catalogue:  5th Edition  (2000)  Howardite
NIPR Catalogue:  2000 Edition  (2000)  Howardite
MetBase:  v. 7.1  (2006)  Howardite
Recommended:  Howardite    [explanation]

This is 1 of 398 approved meteorites classified as Howardite.   [show all]
Search for other: Achondrites, HED achondrites, and Howardites
Writeup from MN J6(1):

Y-790727, 52-2: Howardite

         This specimen was originally listed as a polymict eucrite in the first catalog of the Yamato-79 collection (Kojima and Yanai, 1981), but greenish yellow pyroxenes exposed on the surface of the specimen were confirmed to be orthopyroxene of the howardite-type by single crystal X-ray diffraction. The bulk chemical compositions plot in the middle of the diogenite-eucrite trend in the Al2O3 vs. CaO diagram, and is close to that of cumulate eucrite, Binda.

         This is an angular stone covered by black shiny fusion crust. Irregular deep pits are distributed unevenly, where a slightly stained gray matrix of fine mineral fragments can be seen. At the bottom of a large hole, a relatively coarse lithic clast is observed. Similar vugs have been described in Allan Hills collections.

         The thin section is rich in mineral fragments and shows complex breccia of angular fragments, up to 1.7 mm long, of orthopyroxene, inverted pigeonite, pigeonite, olivine, and plagioclase, with a few lithic clasts, set in a matrix of comminuted pyroxene, olivine and plagioclase. This texture and mineralogy are typical of howardites. Accessory chromite and ilmenite and trace amounts of troilite and nickel-iron are present. The lithic clasts are holocrystalline orthopyroxenite and pyroxene-plagioclase aggregates, and range in texture from dunite, coarse-grained orthopyroxenitic and gabbroic to fine-grained basaltic types. Dark aphanitic clasts are also present.

         Microprobe analyses show a wide range in pyroxene composition. Pyroxenes similar in composition to those in diogenite and eucrites are common, but some pyroxene compositions extend beyond the most Mg-rich diogenite to nearly Ca1Mg81Fe17, and there are inverted pigeonites with Fe/(Mg+Fe) between 0.3 to 0.6. The olivine compositions range from Fa11 to Fa29. Plagioclase ranges from An94 to An82 and averages An88. The presence of orthopyroxene has been confirmed by the single crystal X-ray diffraction. The largest clast in the thin section, 1.7x1.4 mm in size, shows a fine-grained granoblastic texture of orthopyroxene and includes minor fine chromite grains. The texture is similar to some portions of the Y-74013-type diogenites with granoblastic texture. Another recrystallized orthopyroxenite clast 0.8x0.7 mm in size, contains very fine rectangular to lath shaped crystals, but there remains in one area, an unrecrystallized coarse orthopyroxene crystal. No olivine was present. The fine texture suggests a part of orthopyroxene was molten and cooled rapidly to produce the fine-grained texture. More Mg-rich compositions of the melted portion are in agreement with this interpretation.

         A basaltic clast 0.53x0.36 mm in size consists of slightly radiating subparallel laths of alternating pigeonite and plagioclase. The pyroxenes with the eucritic composition show augite exsolution with (001) in common with the host.

Search for this meteorite in the NIPR database (Japan):   
References: Published in Meteorites news : Japanese collection of Antarctic meteorites /Meteorites news : Japanese collection of Antarctic meteorites ,6(1),1-47 (1996-03)
Never published in the Meteoritical Bulletin
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     Catalogue of Meteorites:   (71° 30'S, 35° 40'E)
     Recommended::   (71° 30'S, 35° 40'E)

     This is 1 of 40759 approved meteorites from Antarctica (plus 4494 unapproved names)
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