NORTHWEST AFRICA 6962


Achondrite, ungrouped
(brachinite-like geochemistry, ferroan,
ureilite-like O-isotopic composition)

standby for nwa 6962 photo
Found 2011
no coordinates recorded

A single brown-colored meteorite weighing 59.8 g was found in Northwest Africa and subsequently purchased by M. Farmer from a Moroccan dealer at the 2011 Denver Mineral Show. A sample was analyzed at the University of Washington in Seattle (A. Irving and S. Kuehner) and NWA 6962 was classified as an ungrouped achondrite having some geochemical affinities to the brachinite group, although olivine in this meteorite is significantly more ferroan.

The interior appearance of NWA 6962 has been described as an aggregate of yellowish-brown olivine crystals containing melt inclusions composed of sodic plagioclase + chromite + Ni-free metal, along with an interstitial Na-rich silicate determined by Raman spectra to be nepheline or tridymite. In addition, scattered grains of Ti-poor Al-bearing chromite are present along with minor clinopyroxene (augite), merrillite, and fluorapatite, as well as sparse abundances of FeNi-metal and FeS grains.

Although NWA 6962 shows some mineralogical similarities to brachinites, its geochemical characteristics are inconsistent with a genetic relationship; e.g., Fe-enriched silicates, Fe/Mn ratios, and O-isotopic values (Dunlap et al., 2015). Oxygen-isotopic values for NWA 6962 were ascertained (R. Tanaka, Okayama University, Japan), and the NWA 6962 oxygen three-isotope plot (NWA 6962**URE/BRA/WIN/ACA–LOD) plot near the CCAM line near the resolved fields for ureilites and the acapulcoite–lodranite clan. Notably, the O-isotopic values for NWA 6962 are very similar to those determined by N. Banerjee et al. (Western University, Canada) for the 124 g NWA 7680; see the NWA 7680 oxygen three-isotope plot (NWA 7680**URE/BRA/WIN/ACA–LOD). Since these two meteorites were both purchased in 2011 and have similar O-isotopic values, bulk compositions, and geochemical constitutions, it is considered that they are genetically related (Hyde et al., 2013, 2017).

Further studies of NWA 6962/7680 by Hyde et al. (2017) ascertained the major, minor, and trace elemental compositions, and they concluded there is no obvious relationship to either the ureilites or the acapulcoite–lodranite clan. Since NWA 6962/7680 plot near the CCAM line and show similarities to some CM and CV clasts thought to originate from the interior of these asteroids, it is considered that NWA 6962/7680 could also derive from the deep interior of a primitive carbonaceous chondrite parent body. Further studies are ongoing.

Northwest Africa 6962 shows evidence of low shock and a low degree of terrestrial weathering. The specimen of NWA 6962 shown above is a 0.547 g slice.