Dunite


Northwest Africa 2968

Northwest Africa
Purchased 2005
Achondrite (Dunite with HEDO affinities)

NWA 2968. Width of image is 3 cm. © T. E. Bunch, 2006

History: A 268 g bag of rectangular to blocky, dark brown meteorite fragments was purchased in Erfoud, Morocco in November 2005 collected by nomads in 2004).
Petrography (T, Bunch and J. Wittke, NAU; A. Irving, UWS): Massive olivine-rich rock of very large grain size (17 mm to >25 mm; maximum size is unknown because of the tendency to fracture on cutting). Curved to linear compression and shear fractures are sub-parallel to one of the extinction directions in olivine and are responsible for the common rectangular/blocky habit. Twenty-three pieces (1.8 to 20.1 g) were surveyed. Olivine accounts for > 95 vol. % with small amounts of tiny grains (< 0.03 mm) of orthopyroxene, metal, troilite, and pyrrhotite commonly found within fractures and as rare inclusions in olivine. Large domain offset, isolated mosaicness, and undulatory extinction are prevalent in olivine.
Mineralogy: Equilibrated olivine is Fa7.5±0.2, FeO/MnO = 48 g/g (Cr2O3 and NiO are < 0.03 wt. %); orthopyroxene, Fs6.7Wo1.5, FeO/MnO = 26 g/g; kamacite, Ni = 4.7-6.8; taenite, Ni = 39.1-50.7 wt. %; troilite, Ni = 0.36 wt. %; pyrrhotite, Ni = 1.7-4.7 wt. %.
Oxygen isotopes (D. Rumble, CIW): a cleaned and metal-free sample was analyzed by laser fluorination. Replicate analyses are: δ17O, 1.44 and 1.46; δ18O, 3.08 and 3.64, and Δ17O, -0.178 and -0.212, respectively, and are consistent with HEDO meteorites.
Classification: Achondrite (dunite with HEDO affinities).
Specimens: 22 g, NAU; main mass holder, B. Reed.

Note: HEDO  = "howardites, eucrites, diogenites, olivine diogenites" has been used in the recent literature.

NWA 2968. Photomicrograph of thin section in plane light; width of grain is 22 mm. © T. E. Bunch, 2006

NWA 2968. Backscattered electron image of thin section. Note that most fractures are filled with metal and sulfide. Image © J. H. Wittke, 2006

NWA 2968. Photomicrograph of thin section in cross polarized light (near extinction); note tiny misaligned domains (colors); width of field of view is 5 mm. © T. E. Bunch, 2006