Northwest Africa 14635 (NWA 14635)

(Northwest Africa)

Purchased: 2009

Classification: Brachinite-like achondrite

History: Purchased by Chalom Malka in 2009 from a meteorite dealer in Morocco.

Physical characteristics: Three stones with weathered fusion crust.

Petrography: (D. Sheikh, Cascadia) Sample displays a protogranular texture (Av. grain size=360±230 μm, n=253) predominantly composed of olivine (some grains are elongated and display a notable alignment) (~81 vol. %), orthopyroxene (some regions of the sample display orthopyroxene poikilitically enclosing olivine, chromite, and accessory plagioclase) (~15 vol. %), augite (~3 vol. %), chromite (~1 vol. %), and accessory plagioclase (observed only poikilitically enclosed within either orthopyroxene or chromite), troilite, chlorapatite, merrillite, and Fe-Ni metal (some altered to Fe-hydroxides). A fine-grained intergrowth of orthopyroxene + opaque minerals is observed along the margins of some olivine grains.

Geochemistry: Olivine (Fa_28.0±0.7, range Fa_26.7-29.0, CaO=<0.1 wt. %, Cr₂O₃=<0.1 wt. %, Fe/Mg=0.39±0.01, Fe/Mn=54±2, n=17), Orthopyroxene (Fs_23.9±1.5Wo_1.9±0.5, range Fs_20.5-24.7Wo_0.8-2.2, Fe/Mn=36±3, n=13), Augite (Fs_9.8±0.1Wo_43.5±0.1, range Fs_9.7-9.8Wo_43.4-43.5, Al₂O₃=0.7±0.1 wt. %, Cr₂O₃=0.9±0.1 wt. %, Fe/Mn=25±2, n=2), Plagioclase (An_35.2±0.8Or_1.1±0.1, range An_34.4-35.7Or_1.1-1.2, n=3), Chromite (Cr#=76.1±0.1, Mg#=23.9±2.4, TiO₂=1.3±0.1 wt. %, n=5).

Classification: Achondrite (brachinite-like). While the overall texture, mineralogy, and mineral compositions of the sample are similar to brachinites, the high modal abundance of orthopyroxene, the presence of poikilitic pyroxene-rich areas, the near absence of plagioclase feldspar observed in the sample, the low abundance of CaO in olivine, the low Fe/Mg-Fe/Mn molar ratios of olivine, the fine-grained intergrowth of orthopyroxene + opaque minerals observed at olivine grain boundaries, and the more magnesian compositions of olivine and orthopyroxene indicate that this sample is representative of a brachinite-like achondrite (Goodrich et al., 2017), having similarities to NWA 595, NWA 1500, and NWA 5400.

Specimens: 14.5 g at Cascadia, main mass with Chalom Malka