Lunar Meteorite: Northwest Africa 5000

from The Meteoritical Bulletin, No. 93

Northwest Africa 5000 (NWA 5000)

Morocco
Find: 2007 July
Mass: 11,528 g (1 piece)

Achondrite (lunar, feldspathic breccia)

History: Found in July 2007 in southern Morocco and provided to Adam Hupé in October 2007 by a Moroccan dealer.

Physical characteristics: A single, large cuboidal stone (11.528 kg) with approximate dimensions 27 cm × 24 cm × 20 cm. One side (which appears to have been embedded downward in light brown mud) has preserved regmaglypts and is partially covered by translucent, pale greenish fusion crust with fine contraction cracks. Abundant large beige to white, coarse-grained clasts up to 8 cm across (some of which have been eroded out on exterior surfaces of the stone, likely by eolian sand blasting) and sparse black, vitreous clasts up to 2 cm across (containing irregular small white inclusions) are set in a dark gray to black, partially glassy breccia matrix. One partially eroded clast exposed on an exterior surface contains both the coarse grained beige lithology and the more resistant black, vitreous lithology in sharp contact.

Petrography: (A. Irving and S. Kuehner, UWS) Almost monomict fragmental breccia dominated by Mg-suite olivine gabbro clasts consisting predominantly of coarse-grained (0.5-2 mm) calcic plagioclase, pigeonite (some with fine exsolution lamellae), and olivine with accessory merrillite, Mg-bearing ilmenite, Ti-bearing chromite, baddeleyite, rare zirconolite, silica polymorph, K-feldspar, kamacite, and troilite. Some gabbro clasts have shock injection veins composed mostly of glass containing myriad fine troilite blebs and engulfed mineral fragments. Black, vitreous impact melt clasts consist of sporadic, small angular fragments (apparently surviving relics) of gabbro and related mineral phases in a very fine grained, non-vesicular, ophitic-textured matrix of pigeonite laths (up to 20 microns long × 2 microns wide) and interstitial plagioclase with tiny spherical grains of kamacite, irregular grains of schreibersite and rare troilite.

Mineral composition and geochemistry: Gabbro clasts: plagioclase (An_96.1-98.0Or_<0.1), pigeonite (Fs_32.0-64.5Wo_6.7-13.1; FeO/MnO = 51.1-62.0), olivine in different clasts range from Fa_23.9-24.2, Fa_40.4 to Fa_58.8 (with FeO/MnO = 81-100), chromite [(Cr/(Cr + Al) = 0.737, Mg/(Mg + Fe) = 0.231, TiO₂ = 5.9 wt%], ilmenite (4.1 wt% MgO).

Bulk composition: (R. Korotev, WUSL) INAA of 6 subsamples gave mean values of 5.3 wt% FeO and 0.4 ppm Th.

Classification: Achondrite (lunar, feldspathic breccia). Specimens: A total of 40.2 g of sample, two polished mounts and one large polished thin section are on deposit at UWS. A. Hupé hold the main mass.

Randy Says…

At 11.5 kg, Northwest Africa 5000 is one of the largest single-piece lunar meteorites. It is mineralogically and texturally unique among feldspathic lunar meteorites. The light-colored “gabbro” clasts are impact-melt breccia containing iron-nickel metal from the iron meteorite impactor that formed the breccia. The clasts have the composition of a KREEP-poor (0.9 ppm Sm) gabbronoritic anorthosite (5.1% FeO).  The composition of the whole rock (sawdust: 5.7% FeO, 2.2 ppm Sm) is consistent with a  1:2 mixture the gabbronoritic clasts and a KREEP-bearing, feldspathic regolith with a composition like the NWA 8641 clan of lunar meteorites (5.1% FeO, 2.9 ppm Sm). The regolith component is carried by the dark matrix of the breccia. I estimate that 0.5% of the mass of the meteorite is FeNi metal and that 9% of the iron in the meteorite is in metallic form.

More Information

Meteoritical Bulletin Database

NWA 5000

References

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