Northwest Africa 12434 (NWA 12434)

(Northwest Africa)

Purchased: Nov 2016

Classification: Ordinary chondrite (L3)

History: Purchased in Erfoud, Morocco by Brahim Tahiri and Sean Tutorow while on expedition in November 2016.

Physical characteristics: The type specimen slice is medium to dark brown on cut faces. Well-defined chondrules and metal and sulfide are visible in lighter colored clumps, which are surrounded by darker brown areas lacking metal and sulfide, in which chondrules are not as visible. Larger light colored clasts are visible.

Petrography: (M. Hutson, A. Ruzicka, Cascadia) In thin section (CML1001-2), abundant chondrules, many with sulfide-rich rims, five agglomeratic olivine objects (AO objects), and four large clasts with distinctive textures are visible. Average chondrule size is 0.71 mm (N=73), excluding the four large clasts. Two of the clasts, object 2 (5.7x4.3 mm), and object 11 (2.3x2.2 mm--truncated at edge of thin section), are composed predominantly of zoned aligned olivine crystals and bars set in a matrix of feldspathic material and pigeonite, and rimmed by layer of aluminous low-Ca pyroxene. Object 3 (2.2 × 2.1 mm--truncated by the edge of the section) consists of deformed olivine bars with almost no mesostasis. BSE imaging and mineral analyses show that this clast is equilibrated. The largest (10.8 × 7.6 mm) clast in the section (object 17) has a texture resembling that of shock melt, with equant, zoned olivine and pyroxene grains set in a feldspathic matrix. Object 17 is rimmed by an FeO-rich fine-grained material resembling matrix described by Huss et al. (1981). An oval patch (1.4 × 1.1 mm) of this same material occurs inside the clast as well and contains small multimineralic clasts, including one (20 μm across) composed of kamacite, taenite, and merrillite, and two others (10 and 15 μm across) with cores that contain aluminous spinel, surrounded by layers of fassaitic pyroxene.

Geochemistry: Mineral compositions and geochemistry: (M. Hutson and A. Ruzicka, Cascadia) Olivine (host 19.7±10.1, N=53; object 2 Fa_15.7±4.8, N=27; object 3 Fa_25.3±0.6, N=15; object 11 Fa_19.2±5.1, N=29; object 17 Fa_24.2±8.4, N=15); low-Ca pyroxene (host Fs_15.4±9.3Wo_1.3±1.0, N=26; object 2 rim Fs_8.5±1.2Wo_2.5±0.8, N=25; object 11 rim Fs_7.5±1.7Wo_3.7±0.8, N=8; object 17 Fs_20.3±2.6Wo_1.2±0.6, N=8).

Classification: L3 based on iron contents of olivine and pyroxene in the host and size of chondrules.

Specimens: Cascadia holds 33.9 g in one piece, in addition to three polished thin sections and three mounted butts.