Posted on Leave a comment

NWA 974

E6, ungrouped
(revised in 2008 from EH6 grouping in MetBull 86)
standby for nwa 974 photo
Found April 2001
no coordinates recorded A single highly-weathered stone weighing 2,250 g was found by villagers near Remlia, Morocco, in April 2001. Northwest Africa 974 is composed primarily of enstatite and kamacite, along with minor plagioclase, oldahmite, daubreelite, alabandite, schreibersite, troilite, graphite and silica. It is moderately shocked to stage S4.

Despite its high content of kamacite, long considered to be diagnostic of an EH classification, other compositional characteristics are more consistent with an EL classification. Indeed, it has been demonstrated by Macke et al. (2009) that these two groups do not actually differ in their iron content, and that they are indistinguishable in density, porosity, and magnetic susceptibility as well; however, differences in siderophile, chalcophile, and other mineralogical abundances can be employed to distinguish the two groups. For example, the presence of alabandite rather than niningerite in NWA 974 is typically diagnostic of the EL group, as is the relatively high content of anorthite present. The classifying investigator (A. Jambon, Université Pierre & Marie Curie) believes that these features represent anomalous characteristics attributable to the high metamorphism which the stone has experienced, and he has suggested a classification of EH6 as most appropriate for this stone. Further studies should help resolve the ambiguity in the classification of this enstatite chondrite.

On May 8, 2008 the classification of NWA 974 was revised by the Nomenclature Committee of the Meteoritical Society to reflect a recommendation of E6 chondrite, pending further analyses. The specimen of NWA 974 shown above is a 2.89 g partial slice.

Posted on Leave a comment

NWA 305

(probably EL3)
standby for northwest africa 305 photo
purchased December 2000
no coordinates recorded A 210 g meteorite was purchased by Canadian meteorite dealer D. Bessey in Erfoud, Morocco. Upon cutting, it was considered that it was a particularly nice LL3 and was used to make thin sections. Thereafter, a 34.7 g sample and a thin section were sent to the Russian Academy of Sciences in Moscow for analysis and classification. The preliminary analysis conducted by S. Afanasiev (Vernad) led to the determination that this was an E3 chondrite (Fs1.11, An10.8) with a shock stage of S2 and a weathering grade of W3.

From the preliminary data, including the fact that the chondrule diameter is relatively large compared to EH chondrules, it might be inferred that NWA 305 belongs to the EL chondrite group. Only a few EL3 chondrites are currently known, including several from the Antarctic (e.g., ALH 85199, MAC 88180, and PCA 91020), one from Australia (Watson 007), EL3 xenoliths identified in the carbonaceous chondrite Kaidun (designated Kaidun IV) and in the ureilite Almahata Sitta (designated MS-MU-002), and a few from Northwest Africa (e.g., NWA 3132, NWA 6508, NWA 7406). Therefore, NWA 305 could eventually prove to be an important addition to this highly unequilibrated enstatite meteorite suite. Further information on the classification determinants and the petrogenesis of the E chondrites can be found on the Saint-Sauveur page.

The specimen of NWA 305 shown above is a 5.17 g partial end section. Shown below is a comparison between the E3 chondrite NWA 305 in the top composite photo, and two EL3 chondrites in the bottom composite photo, comprising NWA 6508 (bottom) and NWA 7406 (top). It is obvious that there is a very close similarity in the appearance of chondrules and matrix among all of these meteorites, and it is probable that NWA 305 is an EL3 chondrite.

standby for northwest africa 305 photo
Photos courtesy of Dean Bessey

standby for northwest africa 305 photo
Photos courtesy of Jason Utas; see more here >>