NORTHWEST AFRICA 2824


Eucrite-like basaltic achondrite, ungrouped
(Diogenite in MetBull 95, reclassified to Eucrite-an in MetBull 107)

standby for nwa 2824 photo
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Found 2005
no coordinates recorded

A single stone weighing 485 g was sold to an anonymous buyer in Morocco. A sample was sent for analysis and classification to Northern Arizona University (T. Bunch and J. Wittke), and NWA 2824 was classified as a highly-shocked (S3–5) and brecciated, plagioclase-rich diogenite. Further investigations led to its reclassification by Irving et al. (2018) as an anomalous eucrite.

The meteorite is composed primarily of orthopyroxene (~80 vol%) and plagioclase (as anorthite, ~18 vol%, clasts up to 1.5 cm), along with accessory FeNi-metal, silica, ilmenite, troilite, and rare olivine (Bunch et al., 2009; Irving et al., 2018). The plagioclase exhibits a spherulitic texture indicative of rapid cooling from a melt phase; it has been demonstrated that lunar basalts form a spherulitic texture when cooling at ~20–60°C/hr. The orthopyroxene has a recrystallized texture with indications of a high degree of shock including planar deformation features, mechanical twinning, and exsolution structures. These features are consistent with peak shock pressures of at least 10–15 GPa (Stöffler et al., 1991; Rubin et al., 1997). Sparse tiny vugs are also present.

Northwest Africa 2824 has significant similarities to the vesicular eucrite-like Ibitira including bulk REE abundances and oxygen isotope values (see diagrams below), and it is considered by some that these two meteorites could be related. In light of the potential genetic relationship between Ibitira and NWA 2824, and considering the intense shock experienced by the latter, it may be that Ibitira is actually an impact melt rock rather than a rapidly-cooled basaltic lava (Bunch et al., 2009, #5367). As such, it was suggested that the ubiquitous vesicles present in Ibitira could reflect the former incorporation of solar wind gases in a regolith lithology.

standby for nwa 2824 ree diagram
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Diagram credit: Bunch et al., 42nd LPSC, #1615 (2011)

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Diagram credit: Irving et al., 49th LPSC, #2247 (2018)

The question was raised whether any of the many eucrite and anomalous eucrite-like meteorites now characterized actually derive from dwarf planet (4) Vesta, or instead, represent numerous diverse parent bodies (Irving et al., 2018). Excellent thin section photomicrographs of NWA 2824 made by John Kashuba can be seen on the website Meteorite Picture of the Day for 24 October 2014 and 14 October 2016. The specimen of NWA 2824 shown above is a 4.62 g part slice.