NORTHWEST AFRICA 1821
‘Emerald Extravaganza’


Diogenite
Orthopyroxenite
(≥90 vol% orthopyroxene)

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Purchased January 2003
no coordinates recorded

A single, fusion-crusted stone weighing 40.1 g was found in the Sahara Desert and later acquired by a meteorite dealer in Rissani, Morocco. The meteorite, designated NWA 1821, was subsequently purchased by American collector N. Oakes and submitted for classification to the University of Washington in Seattle (A. Irving and S. Kuehner). A very large stone that is possibly paired with this one is in the collection of a Morrocan dealer, while the 7 gram NWA 1880, classified by A. Greshake and M. Kurz, is most likely paired as well.

This diogenite is an unbrecciated aggregate of coarse, yellow-green, translucent to opaque, orthopyroxene crystals, somewhat similar to the Tatahouine diogenite, but having smaller crystals. In contrast to most fragments of Tatahouine, patches of black fusion crust are distributed over the surface of NWA 1821. In further contrast, this diogenite exhibits a protogranular, crystalline mineralogy, and lacks the ubiquitous black shock veins present throughout Tatahouine. Other constituents present in NWA 1821 include troilite, magnetite, and aluminous ilmenite, along with minor olivine and chromite.

An O-isotopic analysis conducted at the Geophysical Laboratory, Washington, DC (D. Rumble III, 2007) gave a value for Δ17O of –0.269 ‰, within the range of diogenites. To see an alternative classification system for the diogenites and dunites based on mineralogical and petrographical features, proposed by Beck and McSween (2010) and modified by Wittke et al. (2011), click here. The specimen of NWA 1821 shown above is a 0.069 g micromount. A close-up view of a 0.49 g partially cut fragment can be seen here. The photos below show some views of the main mass:

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Photos courtesy of N. Oakes