Northwest Africa 5958 (NWA 5958)

SW Morocco

Found: 2009

Classification: C3.0-ung

History: Purchased by Greg Hupé in September 2009 from a Moroccan dealer in Tagounite.

Physical characteristics: A single, fresh, light-gray stone broken into numerous fragments and weighing 286 g.

Petrography: (T. Bunch and J. Wittke, NAU; A. Irving and S. Kuehner, UWS) The overall texture is fragmental/clastic, with a variety of small objects (mostly 0.05-2.5 mm) set in a dark, fine-grained matrix. Chondrules are predominantly PP, PO, Mg-rich POP and other types. Intact chondrules have multiple (up to 5) accretion rims. Mesostasis is not abundant within chondrules, but where present consists of interlaced quench crystals of fayalite or ferrohortonolite and subcalcic ferroaugite. Some chondrule fragments have discontinuous "veins" of acicular/bladed fayalite. Some PP chondrules contain interstitial grains of carbon (4-16 vol%; grain size = 0.001-0.024 mm; some hexagonal or pseudohexagonal in shape). Carbon grains also are found as fragments in the matrix, and forsterite grains have small carbon clumps. Other rare objects are xenoliths of different fine grained carbonaceous chondrite lithologies, small CAIs and an irregularly-shaped 2.5 mm clast of fragmented calcite.

Geochemistry: The overall compositional range for olivine is Fa_0.15-88 (FeO/MnO = 77-148; Cr₂O₃ = 0.15-0.86 wt.%). Olivine of intact PO chondrule phenocrysts (N = 8) is Fa_0.15-2.5. Olivine in zoned chondrule fragments: rims Fa_25-58, mean Fa₄₆ (Cr₂O₃ = 0.23-0.75 wt.%, mean 0.48 wt.%), cores Fa_10-28 , mean Fa₂₁ (Cr₂O₃ = 0.32-0.86 wt.%, mean 0.54 wt.%). Ferroan olivine is Fa_68-88. Enstatite in PP chondrules (Fs_0.2-2.5Wo_1.3); diopside (Fs_3.4Wo₄₆); subcalcic ferroaugite in enstatite PP chondrule mesostasis (Fs₆₇Wo₁₉). Kamacite (Ni = 5.5 wt.%, Cr = 1.05 wt.%); chromite [Cr/(Cr+Al) = 0.94-0.96]; troilite (Ni = 2.3 wt.%). Oxygen isotopes (D. Rumble, CIW): two acid-washed subsamples analyzed by laser fluorination gave, respectively δ¹⁸O =-8.803, -9.869; δ¹⁷O =-11.398, -12.530; Δ¹⁷O = -6.768, -7.339 per mil.

Classification: Carbonaceous chondrite (ungrouped, 3.0), S1, W1. This is an unequilibrated chondrite with an extremely ¹⁶O-rich bulk oxygen isotopic composition plotting on an extension of the CCAM line.

Specimens: A total of 20.9 g of sample, one polished thin section and a polished thick section are on deposit at UWS. The main mass is held by GHupé.