Northwest Africa 11750 (NWA 11750)

Morocco

Purchased: 2016 May

Classification: C3.00-ung

History: The meteorite was reportedly found near Foum Zguid. It was bought by Pierre-Marie Pelé in Morocco in May 2016 and a subsample was sent to CEREGE for classification. In view of its scientific interest, the whole stone was eventually given to CEREGE by Pierre-Marie Pelé.

Physical characteristics: Black irregular stone. Cut surface reveals a dark homogeneous interior.

Petrography: (J. Gattacceca, B. Devouard, H. Pourkhorsandi, CEREGE; L. Bonal, IPAG) Chondrules and mineral fragments (26 vol%) set in a fine-grained iron-rich matrix (74 vol%, modal abundances by point counting N=204). Average chondrule apparent size 240±170 μm (N=28). Opaque are mostly FeNi metal (both in matrix and chondrules) and sulfides with typical grain size about 10 μm. In the matrix, FeNi metal and sulfides are finely intermixed. Saturation magnetization is Ms=2.39 Am2/kg indicating a bulk metal content of at least 1.1 wt%. Hysteresis properties show the significant presence of tetrataenite in the form of cloudy zone (Gattacceca et al., 2014). XRD over a ~1 cm2 area on a polished section (D. Borschnek, B. Devouard, CEREGE) does not reveal the presence of hydrous phases (serpentine, tochilinite) typically observed in type 2 chondrites using the same experimental setup. The absence of hydrous phases in the fine-grained matrix is confirmed by IR transmission spectra. Raman spectra of the fine-grained matrix reveal the presence of polyaromatic carbonaceous matter characterized by a structural order comparable to type 2 chondrites, thus reflecting a peak metamorphic temperature lower than in the least metamorphosed type 3 chondrites (e.g., Semarkona)

Geochemistry: Olivine Fa_11.9±17.1, range Fa_0.8-45.1, PMD 126% (N=7). Ferroan olivine has Cr₂O₃ 0.24±0.16 wt% (N=3). Orthopyroxene Fs_3.2±2.2Wo_3.8±1.1 (N=3). Kamacite Fe 91.0, Ni 6.7, Co, 2.3 (N=1). Taenite Fe 67.2, Ni 29.6, Co 0.9 (atom%). Oxygen isotopic composition (J. Gattacceca, C. Sonzogni, CEREGE) from analysis of a 1.5 mg aliquot of a powdered 40 mg bulk sample is δ¹⁷O=3.47, δ¹⁸O=14.3, Δ¹⁷O=-4.0, all per mil (linearized, slope 0.5247, analytical uncertainties 0.08‰, 0.12‰, 0.03‰ respectively). Magnetic susceptibility log χ (× 10^-9 m³/kg) = 4.03.

Classification: C3.00-ung. The type 3 derives from the unequilibrated nature, the absence of phyllosilicates and abundance of metal. The subtype 3.00 derives from Raman spectroscopy. The ungrouped designation derives from the oxygen isotopes and petrography.

Specimens: Main mass and type specimen at CEREGE.