Northwest Africa 11118 (NWA 11118)

Western Sahara

Purchased: 2016

Classification: Carbonaceous chondrite (CM2)

History: The meteorite was bought in 2016 from a Moroccan meteorite dealer.

Physical characteristics: A single, black individual partly covered with fusion crust was recovered from the desert near Dakhla City, Western Sahara. The rock is unusually light and diffuses an organic smell.

Petrography: (A. Greshake, MNB) The meteorite appears to be a loosely consolidated aggregation of chondrules, chondrule and mineral fragments and rare CAIs virtually all surrounded by fine-grained dust rims of variable thickness. The different components seem to stick directly together at their respective rims forming a perfect accretionary texture. The meteorite lacks matrix-dominated areas but shows unusually high porosity. Often the fine-grained rims are found empty with the object they had previously surrounded missing. BSE imaging as well as µ-CT scanning of an 1 cm³ volume yield porosities ranging from 30 to up to 38%; the bulk density (volume determined by 3D-scanning) of the meteorite is 1.95 g/cm³. Chondrules are about 60-550 μm in diameter (mean: 171±93 μm, n=43) and dominantly of PO and POP types. Although olivine is highly unequilibrated in chondrules and mineral fragments with Fa_0.3-75.8, low-Ca pyroxene is generally far less Fe-rich with Fs_1.0-4.3. In several chondrules the glassy mesostasis is partly preserved attesting to a rather low degree of alteration. The latter is also confirmed by the low abundance of phyllosilicates and carbonates. Opaque phases include chromite, FeNi-metal (4-6 wt.% Ni), pentlandite and pyrrhotite.

Geochemistry: Oxygen isotopes (K. Ziegler, UNM): material analyzed by laser fluorination gave: δ¹⁸O=6.764; δ¹⁷O=0.670; Δ¹⁷O= -2.901 (all per mil).