NORTHWEST AFRICA 2353


Meta-H
(Achondrite-ung in MetBull 89)
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Purchased January 2004
no coordinates recorded

A single meteorite weighing 580 g was purchased by Astronomical Research Network in Erfoud, Morocco. The stone was analyzed and classified at Northern Arizona University (T. Bunch and J. Wittke) and was initially determined to be a completely recrystallized H chondrite lacking any relict chondrules—an H7 chondrite. The olivine Fa (17.9) and pyroxene Fs (15.6) values are consistent with the H group. Based on the completed O-isotope analysis, it is evident from the oxygen 3-isotope diagram that the ratios plot slightly outside of the main field of H chondrites, but still overlaps the H chondrite and IIE iron parent body.

Since NWA 2353 is a recrystallized, texturally evolved chondrite with elemental ratios and an O-isotopic composition with affinities to the H chondrite group, it is appropriately assigned to the newly proposed group of metachondrites (Irving et al., 2005). Northwest Africa 2353, along with the 678.4 g NWA 3145, 4,200 g NWA 2635, and 1,233 g NWA 2835 (H7) masses, likely constitute a pairing group.

ORDINARY CHONDRITE COMPOSITIONS
  Fa Fs
H 16–20 14.5–18
L 22–26 19–22
LL 26–32 22–26

Northwest Africa 2353 shows evidence of having been very weakly shocked (stage S2, peak pressure of 5–10 GPa), and that it has undergone heavy oxidation since its fall (grade W3). The specimen of NWA 2353 shown above is a 2.8 g partial slice. The top photo below shows a photomicrograph of NWA 2353, while the middle photo shows the complete mass of this metachondrite. The bottom photo shows a magnified portion of this specimen, exhibiting its recrystallized texture, a small melt vein, and a 1 mm-sized vug.


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NWA 2353 viewed in partial crossed-polarized light (base width ~1 cm)
Photo courtesy of Dr. Ted Bunch—Northern Arizona University

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Photo courtesy of Ken Regelman—Astronomical Research Network

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