A single 1,127 g stone with brown fusion crust was found in Northwest Africa and subsequently sold to S. Tutorow in Erfoud, Morocco. A portion of the meteorite was sent for analysis and classification to the University of Western Ontario (Z. Guo and M. Beauchamp) and Washington University (R. Korotev), and NWA 12338 was determined to be a unique ungrouped achondrite.
This fine-grained, unbrecciated basaltic meteorite has an ophitic texture typical for intrusive gabbroic rocks. It is composed of ~100 µm-sized clinopyroxene grains (~55 vol%) enclosing 100500 µm-sized plagioclase crystals (~40 vol%) with minor ~100 µm-sized olivine grains (~4 vol%), along with minor FeNi-metal, troilite, chromite, and silica (~1 vol%). The LREE abundances indicate that a possible unidentified P phase is present. Shock features are observed in the form of mosaicism of plagioclase.
Northwest Africa 12338 has a pyroxene Fe/Mn ratio of 30 (±1), which is at the lower range (2840) of typical eucrites. The meteorite is another anomalous eucrite-like achondrite like Ibitira, Pasamonte, NWA 1240, PCA 82502/91007, Bunburra Rockhole, A-881394, EET 92023, and Emmaville, each of which are geochemically similar to eucrites but have some differences in texture and mineralogy, and they have O-isotopic values that plot in distinct isotopic space above the HED trend (with the exception of NWA 1240 which plots below the HED trend; see diagram below).
Diagram credit: Guo et al., 50th LPSC, #1583 (2019)
Interestingly, it was recognized by Pang et al. (2020) that the Δ17O value for NWA 12338 (0.18 [±0.01]) is very similar to that for both Dhofar 007 (0.173 [±0.010]) and Dhofar 778 (0.160 [±0.054]), and it was suggested that these three meteorites might be genetically related. A Cr-isotopic analysis was conducted for both Dhofar 007 and Dhofar 778 at the University of Science and Technology of China, and the ε54Cr values of 0.46 (±0.09) and 0.51 (±0.07), respectively, support the O-isotopic evidence for a possible common parent body distinct from the HEDs and other anomalous eucrites; Cr isotopes still need to be determined for NWA 12338 (Pang et al., 2020).
Minor and trace element analyses along with MnCr, SmNd, and LuHf isotopic analyses were conducted by Guo et al. (2019) for NWA 12338; results from their investigation are forthcoming. Further information about the anomalous eucrite-like meteorites and their proposed origin from multiple distinct parent bodies can be found on the Pasamonte page. The specimen of NWA 12338 shown above is a 2.67 g part slice, while that below is a 17.55 full slice with brecciation shown courtesy of Dustin Dickens.