NORTHWEST AFRICA 3329


Diogenite
Orthopyroxenite
(≥90 vol% orthopyroxene)

standby for northwest africa 3329 photo

Purchased Spring 2005
no coordinates recorded

A fragmented stone weighing 252 g was collected in Algeria from a similar location as NWA 2968. The fragments were subsequently purchased in Er-Rachidia, Morocco by collector F. Kuntz. A sample of these fragments was analyzed at the University of Washington at Seattle (A. Irving and S. Kuehner) and NWA 3329 was determined to be a diogenite composed primarily of coarse-grained, dark brown orthopyroxene, together with interstitial plagioclase, silica, phosphate, FeNi-metal, and FeS.

The NWA 3329 fragments were subsequently studied by Barrat et al. (2010). Interestingly, some fragments from the batch were found to be identical to the dunitic diogenite NWA 2968, and petrographic evidence indicates that both lithologies were collected from the same location, with both showing similar degrees of weathering. Importantly, other recovered fragments consist of both lithologies together—diogenite and dunite—which are each identical to their respective type samples. Furthermore, trace element studies conducted on both lithologies were found to be consistent with pairing, and their Δ17O-isotopic values are indistinguishable as well (Greenwood et al., 2015). These investigators, in accord with an earlier suggestion by Barrat et al. (2010), interpret the evidence to indicate that both the orthopyroxenite and dunite lithologies are fragments from a common fall, likely as components of a mesosiderite. It was also noted by Greenwood et al. (2015) that the REE pattern previously determined for the diogenite NWA 5613 (Barrat et al., 2010) is virtually identical to that for NWA 3329, presenting further evidence for a possible mesosiderite–HED association.

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Image credit: Greenwood et al., 2015
For an explanation of the diagram components see the open access article in GCA, vol. 169, p. 130 (Nov 2015)

A comparison of reflectance spectra of seven near-Earth asteroids to those of HED-group meteorites revealed that all of the pyroxene mineralogies were consistent with eucrites and howardites, but not to diogenites. Therefore, they suggest that there are no km-sized or larger objects composed strictly of diogenite material, but instead, diogenites might exist as a single component within a mixture of lithologies on the HED asteroid. Beck et al. (2012) identified the first olivine-rich melt material, present in the howardites that constitute the PCA 02009 pairing group. This olivine-rich material was likely derived from harzburgitic and dunitic lithologies exposed on the surface of Vesta.

Further information regarding the origin of the dunitic clasts in our collections can be found on the Vaca Muerta page. 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 photo shown above is a 0.52g fragment of NWA 3329. The photo below is an excellent petrographic thin section micrograph of NWA 3329, shown courtesy of Peter Marmet.

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click on photo for a magnified view
Photo courtesy of Peter Marmet