A single stone weighing 98 g was purchased by B. Fectay in Tagounite, Morocco in 2000. Initial analysis and classification was conducted at Northern Arizona University (T. Bunch and J. Wittke), and NWA 1152 (syn. Tagounite 084) was determined to be a member of the CV3 chondrite group. Subsequent analyses were conducted at the Natural History Museum, UK, while isotopic analyses were completed at The Open University, UK.
Northwest Africa 1152 is primarily composed of highly magnesian type-I PO and POP chondrules (52.2 vol%) having average diameters of 0.9 mm (Smith et al., 2004). It exhibits features consistent with a shock stage of S2, and has experienced moderate to heavy oxidation during its terrestrial residence, resulting in a weathering grade of W2 (W2/3 in MetBull 86). The meteorite has a relatively high matrix content constituting 42.8 vol% and includes minor FeNi-metal phases (0.7 vol%) and rare refractory phases (0.3 vol%) comprising mostly AOAs and spinel-pyroxene aggregates.
Although initially classified as a CV3 chondrite, subsequent studies of NWA 1152 by Smith et al. (2004) found that it has mineralogical and petrographic features that are wide-ranging, exhibiting similarities to both CR and CV chondrites. Perhaps of great significance is the fact that O-isotopic values plot within the CV field. They also found that NWA 1152 is similar in many characteristics to those of the ungrouped C3 chondrite Sahara 00182. In a like manner, it has been demonstrated through compositional, isotopic, and petrographic data by Choe et al. (2010) that Sahara 00182 is closely related (either genetically through parent body origin, or through petrological processes on similar chondritic precursor asteroids) to the C4 chondrite HaH 073, a meteorite previously associated isotopically and mineralogically by Weckwerth and Weber (1998) with the Coolidge/Loongana 001 carbonaceous chondrite grouplet. In consideration of the complex variability that exists among these meteorites, and in spite of the fact that they reflect trends most similar to the CV and CR groups, Smith et al. (2004) concluded that it was most reasonable to classify NWA 1152 (and Sahara 00182) as an ungrouped C3 chondrite. Subsequent in-depth studies of NWA 1152 (and other unusual C chondrites) were carried out by Choe et al. (2010). Despite clear differences in comparison to CV chondrites, and the close similarities when compared to CR chondrites, they concluded that NWA 1152 is most likely an anomalous member of the CV group within a still undetermined subgroup.
Petrographic studies along with O- and Al/Mg-isotopic analyses were conducted by Itoh et al. (2011) on an Al-rich, layered, barred olivine chondrule from NWA 1152 in an effort to constrain the parent body thermal history. Olivine, spinel, and Al-rich diopside grains examined in the host barred olivine chondrule reveal slightly different O-isotopic values compared to those determined for silicates composing the igneous rim, suggesting multiple heating events occurred. The measured 26Mg excess in spinel grains is consistent with chondrule formation at least ~2 m.y. after CAIs, while the lack of such an excess in Al-rich diopside grains indicates an even later crystallization.
Northwest Africa 1152 could prove to be a key piece in solving the parent body conundrum that exists for these several unusual meteorites. The specimen shown above is a tiny cut fragment weighing 10 mg. The photo below shows a large portion of this unusual carbonaceous chondrite in the Fernlea Collection of Rob Elliott.