Northwest Africa 13736 (NWA 13736)

Morocco

Purchased: 2016 Sep

Classification: Ordinary chondrite (LL4)

History: The meteorite was purchased by George Penneff, from Yussef Ait El Caid, on the internet, in September 2016. The owner sent several slices to AUA (November 2021).

Physical characteristics: Ten pieces of this meteorite, for a total known mass of 800 g (before cutting). The color of the meteorite is black. The stones are moderately rusty and covered by an estimated 90% dark fusion crust.

Petrography (S. Xydous; I. Baziotis. AUA): The meteorite displays a brecciated texture, with dark colored clasts embedded within a light gray matrix, locally stained by oxides. The chondrules belong to the BO, POP, RP, PO and cryptocrystalline types. Chondrule fragments are abundant, dispersed within the matrix, while several chondrules retain their original spherical shape along with well-defined accretionary rims. Olivine, low-Ca pyroxene, clinopyroxene and plagioclase (<80 µm) are abundant in the recrystallized matrix, displaying triple-junction contacts. Silicates in the matrix often display undulose extinction. Opaque phases are represented by zoned Fe-Ni metal grains and troilite. Tetrataenite and accessory phosphates (chlorapatite and merrillite) were also identified.

Geochemistry: Data obtained by EPMA examination of carbon-coated thin section. Mineral composition and Geochemistry: Olivine composition in chondrules and in the matrix Fa:28.4±1.5 (n=15). Manganese content in olivine is homogenous ranging from 0.42-0.51 wt. % MnO. Low-Ca pyroxene composition is more variable (Fs_21.2±3.9Wo_2±1, n=14). Low-Ca pyroxene is also represented by the monoclinic pigeonite (Fs_23.3±1.7Wo_13.9±2.1, n=8). High-Ca pyroxene displays a diopside composition (Fs₁₁Wo_42-43, n=3). Plagioclase feldspar is enriched in the albite endmember (Ab_85-86), while inside chondrules plagioclase displays more calcic composition (Ab_17-30). Kamacite (n=4) has Ni content between 5.5-6.5 % wt. Ni and 2.13-3.05 % wt. Co. Taenite (n=4) has zoning in Ni content (29.8-34.5 % wt. Ni) and relatively homogeneous Co (1.06-1.42 % wt.). Troilite (n=3) is stoichiometric with negligible (up to 0.02 % wt.) Ni content. Analyzed phosphates display both merrillite (3.45-3.51 % wt. MgO, n=5) and Cl-apatite (5.85-6.31 % wt. Cl, n=4) compositions.

Classification: Ordinary chondrite (LL4, W2). This is based on olivine composition, pyroxene composition, texture.

Specimens: 760 g at Bulgaria (George Penneff) 39.42 g at NHMV