Northwest Africa 11253 (NWA 11253)

(Northwest Africa)

Purchased: 2017 Mar

Classification: Ordinary chondrite (L, melt rock)

History: Purchased by Aras Jonikas in March 2017 from a Moroccan dealer.

Physical characteristics: A single pale brown stone (40 g) with small vesicles and sparse partly weathered, subspherical metal grains.

Petrography: (A. Irving and S. Kuehner, UWS) Annealed microgabbroic texture (grainsize 0.1-0.4 mm) with vesicles. Some prismatic pyroxene grains are present, but grain boundaries between other grains exhibit triple junctions. Minerals are olivine, very finely exsolved pyroxenes (both low-Ca and high-Ca), oligoclase, chromite, merrillite, chlorapatite, troilite, very sparse but irregularly distributed kamacite (overall <0.2 vol.%, some as partly altered subspherical grains) and minor barite.

Geochemistry: Olivine (Fa_25.2-25.6, FeO/MnO = 47-50, N = 3), low-Ca pyroxene (Fs_20.7-20.9Wo_4.5-4.4, FeO/MnO = 32-35, N = 3), high-Ca pyroxene (Fs_10.9-11.5Wo_38.8-36.8, FeO/MnO = 26-30, N = 3), plagioclase (An_10.1-13.7Or_5.0-2.9, N = 2). Oxygen isotopes (K. Ziegler, UNM): analyses of acid-washed subsamples by laser fluorination gave, respectively, δ¹⁷O 3.843, 4.145, 4.029; δ¹⁸O 5.192, 5.734, 5.524; Δ¹⁷O 1.102, 1.117, 1.112 per mil.

Classification: L-melt rock (vesicular). This specimen apparently has affinities with L chondrites, but the paucity of metal and the presence of exsolution lamellae in pyroxenes are anomalous features.

Specimens: 8.2 g including one polished thin section at PSF; remainder with Mr. A Jonikas.