Lunar Meteorite: Northwest Africa 11223 & 11809
paired stones
| from The Meteoritical Bulletin, No. 106 Northwest Africa 11223 (NWA 11223)(Northwestern Africa) Lunar Meteorite (feldspathic breccia) Physical characteristics: The ROM specimen is one of many pieces found by a meteorite hunter in Morocco. The largest fragments are over 2 kg, with many smaller pieces adding to a total of approximately 10 kg. All specimens observed lacked fusion crust and most were covered in a very thin surface coating of white caliche. However two specimens, which were apparently exposed to the desert winds, showed no caliche, exposing a dark-gray interior with obvious lithic clasts. Petrography: (ROM; K. Hewson, V. Di Cecco, I Nicklin, ROM) In hand sample and thin section the specimen shows lithic and mineral clasts set in a dark-gray, glassy matrix. No vesicles were observed. The largest lithic clast in the ROM specimen is light gray in color and measures 1 × 0.5 cm. Two other relatively large clasts are of a more mixed mineralogy. Geochemistry: (K. Hewson, V. Di Cecco) Feldspar grains have highly anorthitic composition (An90.9-98.6Ab0.0-7.4Or0.1-2.1, n = 94), which is consistent both in the clasts and the matrix. Olivine grains, although rare, are forseritic (Fa28.0-44.5, FeO/MnO = 84.8-119.2, n=15). Pyroxene grains are more common than olivine and are variable in composition. They include augite (En30.2-48.4Fs23.7-26.6Wo2.5-26.6, FeO/MnO = 52.4-61.1, n=5), pigeonite (En40.4-68.0Fs23.3-49.0Wo6.0-19.1, FeO/MnO = 51.8-63.6, n=14) and enstatite (En64.0-65.5Fs31.6-32.1Wo2.5-3.9, FeO/MnO = 57.6-62.9 n=3). Classification: Lunar (feldspathic impact-melt breccia). The largest lithic clast noted has an anorthitic composition, as given by the geochemistry. The two other relatively large clasts have noritic and olivine-noritic compositions based on geochemistry and mineral modality. Mineral fragments are anorthite, clino and orthopyroxenes and rare olivine. Both the lithic and mineral clasts show extensive shock features including mosaicism, planar fracturing and, in the lithic clasts, granularization of the component minerals. Despite the generally uniform caliche coating on most of the specimens the weathering is minimal being confined largely to the exterior but with some very few, very fine fractures containing material similar to the caliche coating which is predominantly barite. Specimens: The ROM holds the main mass of this sample, which originally weighed 28 g. It is now composed of 2 pieces weighing 17.52 and 4.83 g, a thin section, a thin section billet, and 0.20 g of cutting dust. |
| from The Meteoritical Bulletin, No. 107 Northwest Africa 11809 (NWA 11809)Northwestern Africa Lunar meteorite (feldspathic breccia) History: Purchased by Fabien Kuntz in September 2017 from a dealer in Erfoud, Morocco. Petrography: (A. Irving and S. Kuehner, UWS) Breccia composed of angular mineral clasts of anorthite, olivine, orthopyroxene, pigeonite, subcalcic augite and Ti-chromite in a finer grained matrix containing minor barite. Geochemistry: Olivine (Fa30.0-41.3, FeO/MnO = 87-97, N = 3), orthopyroxene (Fs35.7Wo4.2, FeO/MnO = 56), pigeonite (Fs25.2-29.8Wo7.9-10.1, FeO/MnO = 52-63, N = 2), subcalcic augite (Fs15.8Wo30.1, FeO/MnO = 56), anorthite (An92.0-95.0Or0.2-0.1, N = 2). Classification: Lunar (feldspathic breccia). Specimens: 14.11 g including a polished slice at UWB; main mass with Kuntz. |
Randy Says… NWA 11223/11809 is 1 of only 5 lunar meteorites that I know to have a significant (Ce/Ce* <0.8) negative cerium (Ce) anomalies. All are from Northwest Africa (other 4: NWA 10318, NWA 10495, NWA 11182, and Tichiya). negative Ce anomalies have only been observed in meteorite from northern Africa and are caused byn terrestrial weathering processes after the meteorite hits the ground. Curiously, the meteorite does not appear to be more weathered than most NWA lunar meteorites and except for the presence of caliche, the descriptions do not suggest excessive weathering. Nevertheless, I suspect the the Ce anomalies are weathering effects because both stones are contaminated by elements known to be associated with terrestrial chemical alteration in the Sahara Desert. For example, our samples of the two meteorites had 10× and 20× greater concentrations of barium (Ba) than Apollo rocks of otherwise similar composition (Korotev and Irving, 2021). Both, especially NWA 11809, are contaminated with terrestrial arsenic (As), bromine (Br), uranium (U), and light rare earth elements. The negative Ce anomaly is not caused by low tetravalent Ce but by high trivalent light rare earths – La through Sm. For example, Ce/Yb ratios (~7) are normal for feldspathic lunar rocks and soils yet La/Yb ratios (~4.3) are about a factor of 1.7 high. In the figure, Pr and Nd values calculated by interpolation between La and Sm. Dy, Ho, Er, and Tm values interpolated between Tb and Yb. The Gd value is the mean of the La-Sm extrapolation, the Sm-Tb interpolation, and the Yb-Tb extrapolation. |
More InformationMeteoritical Bulletin Database References Hewson K., Tait K. T., Di Cecco V, and. Nicklin I. (2017) The classification of lunar meteorite Northwest Africa 11223. 80th Annual Meeting of the Meteoritical Society, abstract no. 6328. Korotev R. L. and Irving A. J. (2021) Lunar meteorites from northern Africa. Meteoritics & Planetary Science, 206–240. Qin L., Day J. M. D., and Tait K.T. (2020) Oxidative impact processes revealed in Northwest Africa 11223. 51st Lunar and Planetary Science Conference, abstract no. 2318. |