Northwest Africa 2043 (NWA 2043)

(Northwest Africa)

Purchased: 2003 Aug

Classification: Carbonaceous chondrite (CK3)

History: Purchased from a Moroccan dealer in Erfoud for DGregory in August 2003.

Physical characteristics: A single dark green, friable stone weighing 34.9 g.

Petrography: (A. Irving and S. Kuehner, UWS; T. Bunch, NAU) Sparse, relatively small (up to 0.6 mm across), well-formed POP chondrules and ellipsoidal oxide-sulfide-rich objects (0.030-0.140 mm diameter, some within chondrules) in a dark, porous matrix. Olivine in chondrules is compositionally zoned, and pyroxene has pigeonite cores mantled by orthopyroxene. The oxide-sulfide-rich objects are composed predominantly of Cr-bearing magnetite and Ni-bearing pyrrhotite with accessory djerfisherite and chlorapatite. One small object composed of Al-rich, Cr-bearing spinel and chlorapatite may be a type of CAI. The unrecrystallized matrix consists of olivine and lath-like aggregates of plagioclase, aluminous orthopyroxene and aluminous pigeonite, with apparently primary porosity.

Geochemistry: Olivine (Fa_18.4-33.8, mean Fa₃₀, FeO/MnO = 54-124), orthopyroxene (Fs_23.8-24.1Wo_0.4-0.5, FeO/MnO = 79.4-85.1, Al₂O₃ = 4.0-4.6 wt.%), pigeonite cores (Fs_1.7-1.9Wo_11.2-10.7, FeO/MnO = 3.2-3.4, Al₂O₃ = 1.6-2.7 wt.%), plagioclase (An_32.2Or_2.0). Oxygen isotopes (D. Rumble, CIW): analyses of two acid-washed whole rock fragments by laser fluorination gave, respectively, δ¹⁸O = -0.84, -0.97; δ¹⁷O = -3.88, -4.08; Δ¹⁷O = -3.441, -3.576 per mil.

Classification: Carbonaceous chondrite (CK3). The oxygen isotopic composition of this specimen is ambiguous, since it plots near the trends for CM, CO and CK chondrites. Although this composition lies above the trend defined by CK chondrites such as NWA 1665, NWA 1905, NWA 3155 and NWA 4800, the presence of chromian magnetite, lack of metal and lack of primary hydrous phases in NWA 2043 all imply an affinity with CK chondrites rather than CO or CM chondrites.

Specimens: A total of 5.7 g, one polished thin section prepared from it, and one polished mount are on deposit at UWS; the remaining 28.5 g main mass is archived at ROM.