Northwest Africa 2653 (NWA 2653)

Northwest Africa

Purchased: 2004

Classification: CV7

History: Acquired by Rob Wesel in 2004 as part of a parcel of specimens purchased from Moroccan dealers by a consortium of collectors.

Petrography: (A. Irving and S. Kuehner, UWS; T. Bunch and J. Wittke, NAU) Triple grain junction texture devoid of chondrules or chondrule remnants. Mostly composed of fine-grained (<0.5 mm, mean 0.185 mm) polygonal, subhedral grains with the exception of several larger (1.2-3.0 mm) orthopyroxene grains that contain very small (<0.1 mm) olivine inclusions. Minerals are compositionally homogeneous olivine, orthopyroxene, clinopyroxene and intermediate plagioclase (100 to 700 µm) with accessory merrillite, chlorapatite, chromite, troilite, altered kamacite and taenite. Secondary goethite (formed by terrestrial weathering) occurs as thin veinlets and thin coatings on grain boundaries.

Geochemistry: Olivine (Fa_22.0-22.2, FeO/MnO = 65-83, N = 3), orthopyroxene (Fs_19.1-19.6Wo_2.7-2.2, FeO/MnO = 39-43, N = 3), clinopyroxene (Fs_7.8-8.3Wo_44.8-44.5, FeO/MnO = 29-43, N = 2), plagioclase (An_53.2-53.4Or_2.3-2.4, N = 2), chromite (Cr/(Cr+Al) = 84.5), taenite (Ni = 18.9 wt. %). Oxygen isotopes (K. Ziegler, UNM): analyses of acid-washed subsamples by laser fluorination gave, respectively δ¹⁷O -2.333, 1.162, -3.523; δ¹⁸O 2.673, 7.086, 1.227; Δ¹⁷O -3.744, -2.579, -4.171 per mil.

Classification: Carbonaceous chondrite (CV7). This highly recrystallized, chondrule-free material is paired with Northwest Africa 3133; oxygen isotopes for both specimens plot on the trend line for CV chondrites. The bulk elemental abundances, chromium isotopes and tungsten isotopes for NWA 3133 (and by inference for NWA 2653) overlap with corresponding values for Allende and other CV chondrites.

Specimens: 10.2 g including one polished thin section and a polished slice at PSF; the remaining material is with Mr. R. Wesel.