Northwest Africa 14674 (NWA 14674)

(Northwest Africa)

Purchased: 2017 Oct

Classification: Carbonaceous chondrite (CR2, anomalous)

Physical characteristics: one 80 g stone covered by a fresh fusion crust and many small fragments; ~1 mm chondrules in an abundant, dark matrix.

Petrography: The matrix contains abundant framboidal magnetite and phyllosilicates, plus pentlandite, but no tochilinite or chrondstedtite. Chondrules are mostly >500 μm and the biggest is 2 mm across. Average apparent chondrule diameter is 1.3±1.0 mm (n=83). Olivine is fresh in Type I chondrules and pyroxene is partly altered. Olivine in Type II chondrules is partly serpentinized. Chondrule mesostases are replaced by serpentine and chlorite, but diopside dendrites survive. Large metal grains in the matrix are only partly altered. Some chondrules have thick, complex, fine-grained rims, and dark inclusions are abundant, while refractory inclusions are rare.

Geochemistry: Mineral compositions and Geochemistry: Type I chondrule olivine is Fa_1-3 and pyroxene is Fs_2-5. Type II chondrules have olivine Fa_13-31. Kamacite has 6% Ni. Oxygen isotopic composition (J. Gattacceca, C. Sonzogni, CEREGE) from analysis of one acid-washed 1.5 mg aliquot of a powdered 60 mg bulk sample is δ¹⁷O=5.10‰, δ¹⁸O=10.78‰ , Δ¹⁷O=-0.55‰ (slope 0.52, analytical uncertainties 0.08‰, 0.12‰, 0.03‰ respectively).

Classification: Carbonaceous chondrite (CR2-anomalous). Hydrated matrix and partially serpentinised olivine indicate a type 2 chondrite. No crondstedtite and tochilinite are observed as in CM2 chondrites, and chondrule size is much larger than in CM2 chondrites. Large metal grains, complex fine-grained chondrule rims, and abundant dark inclusions are suggestive of CR chondrites, but oxygen isotopes set this meteorite apart from CR2 chondrites. The oxygen isotopic composition is close to that of Al Rais (CR-an) and GRO 95577 (CR1). In a log χ (× 10^-9 m³/kg) vs. δ¹⁸O plot, this meteorite is in the C2-ung 1 defined by Hewins et al. (2021) (see their figure 25). 

Specimens: The type specimen (at MNHNP) consists of 20 g taken from the main mass, which remains with Labenne Meteorites.