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NWA 7030

Meta-LL <!–(Achondrite-ung submitted to MetBull)
–> standby for nwa 7030 photo
click on photo for a magnified view Found 2011
no coordinates recorded A single fusion crusted stone weighing 224 g was found in Northwest Africa and subsequently sold to meteorite dealer G. Hupé in Zagora, Morocco. A sample was submitted for analysis and classification to the University of Washington in Seattle (A. Irving and S. Kuehner), and NWA 7030 was determined to be a metachondrite with similarities to the LL chondrite group.

Northwest Africa 7030 is a texturally evolved meteorite that lacks any relict chondrules, and it exhibits an overall texture akin to a fine-grained igneous cumulate. The predominant lithology was described as consisting of olivine, clinopyroxene, sodic plagioclase, chromite, troilite and taenite. A less prevalent greenish-colored, igneous-textured lithology is also present. Its composition is different from that of the primary lithology in that it contains interstitial potassic-feldspar (sanidine) along with albitic plagioclase, and it contains much less troilite. Another difference is the presence of orthopyroxene and rare kamacite in the minor lithology (Fernandes et al., 2014).

The O-isotopic composition of NWA 7030 was analyzed at Okayama University (R. Tanaka) and it was shown to plot within the LL chondrite field. Bulk density measurements for NWA 7030 were conducted at the University of Central Florida (D. Britt [UCF]; B. Macke and G. Consolmagno [Vatican]) employing both pycnometer and glass bead methods (results forthcoming).

Although NWA 7030 was shown to have affinities to the LL-chondrite group, it has many anomalous features that make it unique, and therefore, could be considered as ungrouped. The K–Ar age was determined for the minor lithology, and the results indicate the occurrence of two separate impact heating/degassing events that have disturbed this isotopic chronometer: one at ~4.12 b.y. and the other at ~2.39 b.y. (Fernandes et al., 2014).

The specimen of NWA 7030 shown above is a 0.77 g end section. The top photo below shows the fresh fusion-crusted mass, while the bottom photo shows the interior of a 15.62 g slice with both lithologies—photos courtesy of Greg Hupé.



Photos courtesy of Greg Hupé—Nature’s Vault


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NWA 5297

Meta-LL
Possibly brachinite-related
(Primitive achondrite, ungrouped in MetBull 98)

standby for nwa 5297 photo
Found March 2008
no coordinates recorded Nine small stones having a combined weight of 130 g were found near Alargoug, Morocco, and subsequently sold in June 2008 to meteorite dealer G. Hupé. A sample was submitted for analysis and classification to the University of Washington in Seattle (A. Irving and S. Kuehner), and NWA 5297 was determined to be a completely metamorphosed chondrite (metachondrite) with similarities to the LL chondrite group.

Northwest Africa 5297 is composed of olivine, orthopyroxene, and very sodic plagioclase, along with minor taenite and Ni-bearing troilite. It is a texturally evolved meteorite that exhibits a poikiloblastic structure (finer-grained inclusions of one mineral embedded within larger crystals of another mineral) and lacks any relict chondrules.

The O-isotopic composition of NWA 5297 was analyzed at the Carnegie Institute in Washington D.C. by D. Rumble III, and subsequently by Greenwood et al. (2017). This meteorite was shown to have affinities to the LL-chondrite group (see diagram below). standby for o-isotopic diagram
Diagram credit: Greenwood et al., Chemie der Erde, vol. 77, p. 24 (2017)
‘Melting and differentiation of early-formed asteroids: The perspective from high precision oxygen isotope studies’
(open access: http://dx.doi.org/10.1016/j.chemer.2016.09.005)
However, NWA 5297 has a greater abundance (~10 vol%) of FeNi-metal than would be expected for an LL-chondrite parent body that had experienced a high degree of metamorphism. Furthermore, it was determined that the the olivine composition of NWA 5297 lies outside the range for equilibrated LL chondrites, and the meteorite was recognized by Dunlap et al. (2015) as being similar to the brachinites. They also found that silicates in NWA 5297 plot in the brachinite field on an Fe/Mn vs. Fe/Mg coupled diagram.

Based on Al–Mg systematics, Dunlap et al. (2015) calculated an upper limit of <4.5679 b.y. ago for the timing of Al/Mg fractionation during differentiation on the NWA 5297 parent body. With all of these characteristics taken together, NWA 5297 might be considered as ungrouped, but possibly related to the brachinites. The specimen of NWA 5297 shown above is a 2.78 g partial slice.