NORTHWEST AFRICA 12319


Achondrite, ungrouped
Dunite breccia
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Found 2018
no coordinates recorded

Thirteen partially crusted fragments and other broken bits, having a combined weight of 35.3 g, were found in 2018 and subsequently purchased by A. Mazur. Samples were sent for analysis and classification to the Bartoschewitz Meteorite Laboratory (R. Bartoschewitz) and the Geological and Mineralogical Museum at the University of Kiel (P. Appel and B. Mader). Following an O-isotopic analysis conducted at the University of Göttingen (A. Pack), it was determined that NWA 12319 should be classified as an ungrouped achondrite.

In 2015, prior to the purchase and classification of NWA 12319, a 148 g stone designated NWA 12217 was purchased by J. Piatek. The meteorite was analyzed at the University of New Mexico (C. Agee), including an oxygen isotope analysis (K. Ziegler), and it was classified as an ungrouped achondrite, dunite breccia (see photo below).

Cut Slice of NWA 12217
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Photo credit: Vaci et al., 50th LPSC, #1175 (2019)

Besides NWA 12217, a 3,930 g stone designated NWA 12562 was found in 2017 and subsequently purchased in May 2018 by Z. Ke. The meteorite was analyzed at the Central South University in China (X. Gu) and the University of New Mexico (Z. Vaci and C. Agee; oxygen isotopes by K. Ziegler), and it was also classified as an ungrouped achondrite, dunite breccia (see photo below). The MetBull description of NWA 12562 indicated many similarities to NWA 12217.

Complete Mass of NWA 12562
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Photo courtesy of Zuokai Ke

Even though some textural differences exist among these three independently classified meteorites, and while they encompass a broad range of major element and O-isotopic compositions (see diagram below), it is still considered likely that they all represent a common pairing group from a unique parent body. Other material in the possession of A. Habibi, including a crusted fragment weighing 129 g and numerous small fragments weighing together 114.5 g, are part of this pairing group; however, this lot has not yet been given a NWA-series designation.

Oxygen Isotopes: NWA 12217 (red) / 12319 (pink) / 12562 (orange)
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Diagram adapted from Meteoritical Bulletin Oxygen Isotope Plots

Each of these meteorites have similar petrographic characteristics and have been described as fragmental breccia, with the compositional variability suggesting a polymict breccia (Vaci et al., 2019, #6459). The meteorites are composed primarily of large (up to cm-sized), angular, cream-colored olivine grains that are crosscut by dark shock fractures. The olivines are embedded in and possibly sintered together with darker gray comminuted material (down to µm-sized). Olivine has a modal abundance of 85–93% (NWA 12562 and NWA 12217, respectively) consistent with a dunite (>90%). Other phases present in minor or trace abundances include pyroxene, troilite, chromite, FeNi-metal, tridymite, andesine and alkali feldspar, schreibersite, pentlandite, merrillite, fluorapatite, and ilmenite. Secondary Cr-bearing symplectites associated with silicates were observed in both NWA 12217 and NWA 12562. On a coupled Fe/Mn vs. Fe/Mg diagram, Vaci et al. (2019) demonstrated that NWA 12217 olivines have values that are consistent with formation as a cumulate of an igneous differentiation process involving fractional crystallization, rather than as a partial melt residue.

It is noteworthy that the unique 1.1 g olivine-rich (dunitic/harzburgitic?) achondrite QUE 93148, originally classified as a lodranite, has O-isotope and trace element data which has led some investigators (Goodrich and Righter, 2000; C. Floss, 2003) to suggest it might instead be derived from the deep mantle of the HED parent body. However, due to its lower Co and Ni abundances than what would otherwise be expected for an olivine-rich mantle lithology or magma ocean cumulate, other teams (Shearer et al., 2008; Shearer et al., 2010) have suggested that QUE 93148 originated on a distinct planetary body such as that of the main-group pallasites. Furthermore, Hahn et al. (2018) studied orthopyroxene–chromite symplectites in QUE 93148 as well as its geochemistry, and they contend that the meteorite is probably a mantle residue derived from a high degree of melting and is likely is related to harzburgite clasts present in some howardites. Yet, the symplectites in QUE 93148 have been compared by Vaci et al. (2020, #1751) to those in NWA 12217 and NWA 12562, and they argue that the similar mineralogy and petrology of these meteorites suggest a possible genetic link.

The specimen of NWA 12319 shown above is a 0.87 g fragment. This specimen is also shown below with two larger fragments and the main mass representing this NWA classification.

NWA 12319 Fragments: (l–r) 4.28 g, main mass, 0.87 g, 3.74 g
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Photo courtesy of Alan Mazur