Northwest Africa 11024 (NWA 11024)

(Northwest Africa)

Purchased: June 2014

Classification: Carbonaceous chondrite (CM, anomalous)

History: One stone of 4.69 g was purchased in Ensisheim from a Moroccan dealer in June 2014 by Sergey Vassiliev.

Petrography: S. Ebert, A. Bischoff (IfP), D. Harries (UJena): The chondrite consists of 32% chondrules and chondrule fragments (mainly PO and POP), about 54% fine-grained opaque matrix, 9.5% fine-grained dust rims, and 1.2% refractory inclusions (CAIs). Most chondrules have a size of about 150-300 µm and many are surrounded by fine-grained dust rims. Most CAIs are fine-grained, fluffy, spinel-rich inclusions. Many are rimmed by fine-grained dust. Sulfide and some metal present. Most of the metal grains have been destroyed by terrestrial alteration. Carbonate grains are absent. TEM investigations (D. Harries, UJena) of several areas and lithologies (fine-grained dust rims, matrix portions) do not show any phyllosilicates. Instead, the fine-grained inter-chondrule materials mainly consist of nano-crystalline Fe-rich olivine and troilite and small Ni-rich Fe,Ni-metals, which are unaffected by aqueous alteration.

Geochemistry: Mineral composition and geochemistry: S. Ebert, A. Bischoff (IfP) A. Pack (UGött): Most chondrule olivines have Fa_<4, but also chondrules and chondrule fragments with olivine of higher Fa-content (up to Fa₆₃) exist. Similarly, most low-Ca pyroxenes are enstatites (Fs_<2), but also some low Ca-pyroxenes with somewhat higher Fs-contents exist (e.g., Fs_5-13), and  a compound chondrule with abundant low-Ca pyroxene of ~Fs₄₅ was observed. The remaining unweathered large metal grains are Ni-poor (~6 wt% Ni). Two bulk measurements of oxygen isotopes plot with δ¹⁸O = 6.85 ‰ and δ¹⁷O = -1.6‰ and δ¹⁸O = 6.07 ‰ and δ¹⁷O = -1.44 ‰, respectively, at the ¹⁶O- and ¹⁸O-rich edge of the CM-field, clearly distinct from the O-isotope field of the CO3 chondrites.

Classification: The textural observations suggest a CM classification of this rock. This is supported by the O-isotope composition. The lack of hydrous minerals and carbonates suggests a type 3 petrologic type. The olivines do not show undulatory extinction. Thus, the rock is unshocked (S1). Since most of the Ni-poor metal has been destroyed, the sample is strongly weathered (W3).

Specimens: IfP holds the main mass (2.5 g remaining of the 4.7 g) and 2 thin sections.