Northwest Africa 7493 (NWA 7493)
Lunar meteorite (feldspathic breccia)
Physical characteristics: Six matching separate stones (total weight 503 g), consisting of two larger stones (341 g and 146 g) and four smaller pieces (total 16 g). Irregular, desert-weathered exterior with heavy patina in places and visible light and dark patches. Sawn slices exhibit a brecciated texture dominated by medium gray, tan and white lithic clasts plus white feldspar grains (up to 5 mm across) set in a sparse, darker gray matrix. Some thin veins of terrestrial weathering products visible.
Petrography: (C. Agee, UNM; A. Irving, UWS; R. Mills, JSC) Microprobe examination of five polished mounts and a complete slice shows this specimen to be a fragmental breccia composed primarily of quenched melt clasts and calcic plagioclase grains occurring in a wide range of grain sizes. There are numerous scattered olivine and zoned pyroxene grains throughout, rare grains of exsolved pigeonite, ilmenite, Ti-chromite, troilite, silica polymorph and iron metal. Shock melt domains are common containing plagioclase grains set in a matrix of quench crystals. A single “granophyre” clast (100 microns across) composed of intergrown K-feldspar+silica was observed. Secondary barite and iron oxide/hydroxide were detected.
Geochemistry: (C. Agee and M. Spilde, UNM; A. Greshake and P. Czaja, MNB; A. Irving and S. Kuehner, UWS). Olivine Fa39.6±7.8, Fe/Mn=94±8, n=49; low-Ca pyroxene Fs37.4±7.0Wo4.7±1.6, Fe/Mn=57±8, n=30; pigeonite Fs34.4±9.4Wo12.9±4.0, Fe/Mn=60±5, n=15; high-Ca pyroxenes Fs26.9±10.9Wo38.4±4.6, Fe/Mn=58±9, n=15; plagioclase An96.6±0.6Ab3.3±0Or0.2±0.15, n=17. Bulk composition (R. Korotev, WUSL). INAA on 18 subsamples gave the following mean values: Na2O=0.331, CaO=16.3, FeO=4.52 (all wt%); Sc=8.67, Cr=587, Co=12.48, Ni=81, La=2.09, Nd=3.2, Sm=0.984, Eu=0.772, Lu=0.111, Hf=0.63, Ir=0.0037, Au=0.0021, Th=0.29, U=0.16 (all ppm).
Oxygen Isotopes, laser fluorination (K. Ziegler, UNM), 12 analyses on 5 acid-washed aliquots gave mean values d17O=2.963±0.126, d18O=5.646±0.316, Δ17O=-0.018±0.06 (linearized, all permil).
Classification: Achondrite (lunar, feldspathic breccia)
Specimens: A total of 30 g of material including two probe mounts are on deposit at UNM. The remainder is divided between Dr. J. Piatek and Mr. M. Morgan, with Dr. J. Piatek holding the main portion of the largest stone and the other five stones.
Compositionally, Northwest Africa 7493 is a typical feldspathic lunar meteorite.
Meteoritical Bulletin Database
Agee C. B., Korotev R. L., and Irving A. J. (2013) Petrology and bulk composition of two lunar fragmental breccias: Northwest Africa 7493 and Northwest Africa 7611. 44th Lunar and Planetary Science Conference, abstract no. 2629.
Korotev R. L. and Irving A. J. (2021) Lunar meteorites from northern Africa. Meteoritics & Planetary Science, 206–240.