Achondrite, ungrouped
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Purchased 2021
26° 2' 20" N., 9° 16' 45" W.

A single stone lacking fusion crust and weighing 12,400 g was found in Western Sahara close to the northern border of Mauritania (Google Earth image). The meteorite was subsequently purchased by Said Muftah Bachir and a sample was sent for analysis and classification to the University of New Mexico (C. Agee, A. Ross, and K. Ziegler) where Al Bir Lahlou 001 was classified as an ungrouped achondrite; specifically, a plagioclase-rich norite based on IUGS taxonomy.

NORITIC: orthopyroxene + <5 vol% olivine + >10 vol% plagioclase

Diogenite Classification Ternary Diagram
Al Bir Lahlou 001 denoted by blue square

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Diagram adpted from Irving et al., 47th LPSC, #2264 (2016)

Compared to the analyzed diogenites, Al Bir Lahlou 001 contains an anomalously high anorthitic plagioclase (An97.9 [±0.1]) content of 60 vol%, along with 35 vol% orthopyroxene and minor abundances of olivine (~100 µm inclusions in pyroxene), nearly pure Fe-metal, and Cr-spinel (Agee and Ross, MetBull 110). For example, the ABL 001 norite is unique compared to the noritic diogenite NWA 10388, described by Irving et al. (2016 #2264) as containing 72.2 vol% orthopyroxene and 25.1 vol% plagioclase as bytownite (An85.9–88.0). In addition, they identified a noritic clast in the shock-melted feldspathic diogenite NWA 8744 that has a high plagioclase content of 40 vol%, but which is still lower than that of ABL 001. In addition, Irving et al. (2014 #5199) analyzed other diogenites with relatively high modal abundances of calcic plagioclase, including noritic diogenite NWA 6928 and feldspathic diogenite NWA 8000 with 19 vol.% (An92.9–94.2) and ~10 vol.% (An88.1–89.0), respectively, and also a noritic clast in polymict diogenite NWA 6945 containing ~20 vol.% (An95.7–99.9) calcic plagioclase.

The oxygen isotopic composition of Al Bir Lahlou 001 (3 subsamples by K. Ziegler, UNM) plots very close to the anomalous eucrite NWA 8671, which has more negative Δ17O values than all other analyzed eucrites (see diagram below). A comparison between ABL 001 and diogenites based on mineralogy, geochemistry, and O-isotopic composition supports the presumption that it derives from a separate parent body.

Oxygen Isotope Plot For Al Bir Lahlou 001
Denoted by white circle located next to NWA 8671

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

The question was raised whether any of the many eucrite, anomalous eucrite-like, and diogenite meteorites now characterized actually derive from dwarf planet (4) Vesta, or instead represent numerous diverse parent bodies (Irving et al., 2018). The specimen of Al Bir Lahlou 001 shown above is a small representative 2.72 g slice sectioned by C. Zlimen, which features milky-white plagioclase grains intermixed with green orthopyroxene grains. The excellent photo of Al Bir Lahlou 001 at the top below shows a close-up of the natural exterior and cut face of the meteorite courtesy of S. Bachir, while the bottom photo shows a large complete slice in high-resolution courtesy of C. Zlimen.

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Photo courtesy of Said Muftah Bachir

standby for al bir lahlou 001 mm photo
click on photo for a magnified view

Photo courtesy of Craig Zlimen

See a YouTube video of a 116.24 g translucent slice of Al Bir Lahlou 001 shown by Marcin Cimala of PolandMet.