Northwest Africa 7812 (NWA 7812) meteorite, Mauritaniai

Regional Level Types
Northwest Africa 7812 (NWA 7812) meteorite	Meteorite Fall Location
Mauritania	Country

Angrite, quenched
Find, 2013; 46.2 g, single stone

The Northwest Africa 7812 meteorite (NWA 7812) is a single, rounded, black, fine-grained stone purchased in Erfoud, Morocco. The stone is much more magnesian than most other angrites. Small strongly-zoned olivine phenocrysts (0.3-0.8 mm long) and fairly homogeneous clinopyroxene phenocrysts (up to 0.45 mm long) are set in a fine-grained groundmass. The groundmass is dominated by bladed and intergrown grains of kirschsteinite, anorthite (An100), Ca-rich clinopyroxene, and ulvöspinel. Minor troilite is also present. Inclusions of Cr-Al spinel and pentlandite are found within olivine. Vesicular features were noted in several instances. Secondary barite is present in the groundmass and in microfractures. Calcite was noted as well.

NWA 7812 is one of 15 recovered angrite meteorites (as of July 2015). Meteorites like Mg-rich NWA 7812 and the more recently recovered 2014 NWA 8535, a dunite, are gradually making it clear that the angrite geochemical group of meteorites have sampled a surprisingly diverse set of Ca-rich mafic and ultramafic environments. A K-Ar age of ~3 Ga for NWA 7812 may be due to an ancient degassing event (probable collision). A reported cosmic-ray exposure age (CRE) of ~20-22 Ma does not overlap with CRE ages determined for other angrites. The surprising range in CRE ages for the angrites (<1 Ma—>50Ma without major clusters) appears to provide a parallel physical analog to the still emerging petrographic and mineralogical complexity of this set of ancient stones.

NOTE: We follow Meier et al. (2013) in listing Mauritania as the original site of the meteorite's recovery. As the geographical coordinates are presently unknown to the meteoritical community, the location is formally designated simply as Northwest Africa at the Meteoritical Bulletin Database.

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