Northwest Africa 13124 (NWA 13124)

Morocco

Purchased: 2014

Classification: Carbonaceous chondrite (CK3)

History: Sample was purchased at the Denver mineral show in 2014 from Sidi Mohamed Ismaily, who acquired it from Morocco. Sample is catalogued at the Royal Ontario Museum as M58927.

Physical characteristics: Rounded individual with 15% dark fusion crust remaining. Extensive broken and weathered surfaces reveal a chondritic gray meteorite, with chondrules up to 3 mm in size. Magnetic susceptibilty of a 4.47 g cut endpiece is log χ (× 10^-9 m³/kg) =4.04.

Petrography: Cut surfaces (9 cm2) show a grey, porous matrix containing dark, well-defined chondrules and large, 3 mm CAIs, with matrix comprising 60 vol%. In thin section, chondrules are well spaced (20 vol%) in a dark, porous matrix and readily delineated, averaging 796±490 µm in diameter (n=64). CAIs account for approximately 10 vol% of the sample. AOAs make up approximately 7 vol% of the sample. Metal is absent. No phyllosilicate is present in the rock. Chondrule mesostasis is typically microcrystalline and locally glassy. Olivine grains are clean and show sharp extinction. There is little evidence of weathering phases. In reflected light, sulfide (1 vol%) is finely disseminated in matrix and also present as larger rounded grains in chondrules. Magnetite is present as abundant isolated grains in matrix, as inclusions in some chondrules and in chondrule rims. In BSE images, matrix consists mainly of tiny elongate olivine grains (10 µm length) and larger subhedral olivine (up to 50 µm), all with a uniform Fe-rich composition. Olivine in chondrules is typically zoned to Fe poor cores. Magnetite typically has a spongy appearance as aggregates and has a common association with troilite and pentlandite, where those sulfide phases are present.

Geochemistry: EPMA: Olivine Fa_26.98±16.94 (n=16), chondrule olivine Fa_19.88±15.90 (n=11), matrix olivine Fa_42.61±0.78 (n=5), matrix olivine NiO wt% = 0.35±0.02; Ca-poor pyroxene Fs_1.16±0.21, Wo_0.75±0.15 (n=8); Ca-rich pyroxene Wo_46.14±7.53 and Fs_1.11±0.39 (n=8). Magnetite composition key elements (all wt%): Cr₂O₃=1.83±1.23, TiO₂=0.20±0.19, Al₂O₃=2.10±0.57, NiO=0.49±0.43 (n=21).

Classification: CK3, low shock, W0. CK3 is indicated by: matrix of small, equilibrated Fe-rich olivine grains and rounded magnetite aggregates, and chondrule olivine with variable composition, zoned to low Fe cores. EPMA matrix olivine NiO wt% >0.30 and magnetite compositions consistent with CK chondrite.

Specimens: Type specimen ROM; main mass Gregory