Several fusion-crusted stones having a combined weight of 380 g were found near Foum Zguid, Morocco and purchased by R. Chaoui. These were subsequently acquired by a number of meteorite dealers, including material purchased by G. Fujihara from R. Chaoui's brother. Sample analyses were conducted at the University of Washington in Seattle (A. Irving and S. Kuehner), Arizona State University (L. Garvie), and the University of New Mexico (oxygen isotope analysis; K. Ziegler). The meteorite was classified as an ungrouped carbonaceous chondrite.
The silicates identified in NWA 8781 include olivine, orthopyroxene, and diopside, along with the opaque minerals kamacite and troilite. The geochemistry writeup in MetBull 107 states that the ferroan olivine component contains 0.20.4 wt% Cr2O3, which is consistent with a subtype 3.0 (Ruggiu et al., 2021 and references therein). The fine-grained matrix material constitutes ~50 vol%, and no phyllosilicates were observed. Chondrules are very small (210 [±60] µm) compared to those in CV and CK chondrites. The apparent absence of CAIs is also inconsistent with CV as well as CO chondrites, and the lack of magnetite is inconsistent with CK chondrites. In addition, the O-isotope composition of NWA 8781 is more 16O-rich than that of CM chondrites and plots in a space distinct from other known carbonaceous chondrite groups, but is similar to the C3-ungrouped Telakoast 001 and NWA 12416, and the C2-ungrouped NWA 13167 and NWA 13479 (see diagrams below).
Diagram from MetBull 107
Diagram from MetBull 110
Diagram from MetBull 108
Diagram from MetBull 109
Diagram from MetBull 109
Diagram credit: Greenwood et al., GCA, vol. 277, p. 381 (2020, open access link)
'Linking asteroids and meteorites to the primordial planetesimal population'
Comparative analyses of the known asteroid types and a suite of ungrouped and rare meteorites in multiple forms (bulk, powder, polished section), including the ungrouped carbonaceous chondrite NWA 8781, were conducted by Ruggiu et al. (2021) utilizing petrographic, spectroscopic, and albedo data. They concluded that the best matches to this meteorite are the Xe- and Xk-type asteroids (see diagram below).
Comparison of Meteorite and Asteroid Spectra
Diagram credit: Ruggiu et al.Icarus, vol. 362, art. 114393 (2021, open accesslink)
'Visible-infrared spectroscopy of ungrouped and rare meteorites brings further constraints on meteorite-asteroid connections'
Northwest Africa 8781 has experienced a low degree of terrestrial weathering, and it has features indicative of very weak shock (S2). The specimen of NWA 8781 shown above is a 0.77 partial slice photographed with a cm-scale cube, courtesy of Gary Fujihara.
Read the Micro Visions article for September 2020 about NWA 8781 in Meteorite Times Magazine, written by John Kashuba and including his always excellent thin section photomicrographs.