Northwest Africa 13966 (NWA 13966)

(Northwest Africa)

Find: 2016

Classification: HED achondrite (Eucrite, monomict)

History: A single stone acquired by Michael Farmer from a Moroccan meteorite dealer at the 2016 Tucson Gem and Mineral show.

Physical characteristics: (L. Garvie, ASU): Blocky, relatively fresh, fusion crusted stone. A 4 × 3 cm polished end-piece shows a coarse-grained texture, with mm-sized plagioclase and pyroxene. One 2 × 1 cm clast shows several prominent olive-green lath-shaped grains to 1 cm. Sparse, <0.2 mm, metal grains are scattered across the section.

Petrography: (M. Marquardt, J. Brown, A. Wittmann, ASU): Fine-grained breccia with coarse ophitic clasts set in the fragmental matrix. The specimen is composed primarily of equal proportions of pyroxene and calcic plagioclase. Plagioclase in the sample is intensely fractured. Throughout the coarse-grained clasts are large, acicular SiO₂ laths upwards of 2 mm × 0.04 mm. Pyroxene exhibits sub-µm exsolution lamellae (low-Ca lamellae with high-Ca host). Additionally, some pyroxene show relict concentric zonation with a core composed of augite with a rim composed of pigeonite. The interstitial space between the coarse pyroxene-plagioclase clasts is primarily comprised of fine-grained intergrowths of SiO₂, pyroxene, fayalite, and troilite. Accessory minerals are fayalite, ilmenite, chromite, troilite, Fe-metal, fluorapatite, merrillite, and zircon.

Geochemistry: (A. Wittmann, M. Marquardt, J. Brown, ASU): Microprobe analysis of the polished mount shows heterogeneity among pyroxene throughout the sample. Low-Ca pyroxene En_43.6±21.1Fs_48.3±19.5Wo_8.1±5.8 Mg#=47.4±21.8 (n=31); High-Ca pyroxene En_26.3±5.9Fs_49.1±7.8Wo_24.6±9.1 Mg#=34.9±6.4 (n=17); Plagioclase An_85.5±9.8Ab_13.5±8.6Or_0.96±1.2 (n=39); SiO₂ (up to 0.52 wt% Al₂O₃ , n=31).

Specimens: 25 g at ASU.