Northwest Africa 2202 (NWA 2202)

(Northwest Africa)

Purchased: 2004

Classification: HED achondrite (Eucrite, polymict)

History: Purchased by DGregory in 2004 from D. Bessey, who obtained it from Morocco that year.

Physical characteristics: A 140 g individual with a dark fusion crust covering 2/3 of the meteorite and a grey, brecciated interior. Bulk physical properties (P. McCausland, UWO): An 11.2 g slab has a grain density of 3.19 g/cm³, a bulk density of 2.89 g/cm³ (giving calculated porosity of 9.5%) and magnetic susceptibility log χ = 3.20.

Petrography: (P. McCausland and R. Flemming, UWO). A 2.7 cm² polished thin section shows a variety of subangular brecciated lithic and crystalline clasts ranging up to 3 mm diameter, set in a matrix of sub-0.1 mm plagioclase, Ca-rich pyroxene, Ca-poor pyroxene, accessory Fe-sulphide, chromite, ilmenite and interstitial Fe,Ni metal. Pyroxene commonly exhibit planar deformation features and mottled-to-mosaic extinction in crossed polarizers. Lithic clasts have a dark, fine-grained matrix that by SEM-EDX has a similar composition to the host meteorite matrix. The lithic clasts contain low-Ca, Mg-rich pyroxene megacrysts, one of which is mm-sized and zoned to Fe-rich rims. Carbonate weathering veins to 0.1 mm width are common, lying alongside of and often completely enclosing the lithic clasts, separating them from matrix.

Geochemistry: (R. Flemming, J. Renaud, UWO) Ca-rich pyroxene (Fs_38.4±5.4Wo_28.4±5.8, n=19; FeO/MnO = 32.4); Ca-poor pyroxene (Fs_53.6±1.3Wo_6.7±2.2, n=6; FeO/MnO = 30.8); Ca-poor pyroxene in dark clast (Fs_31.3Wo_6.2, n=2; FeO/MnO = 29.3; Fe-rich rim Fs_58.6Wo_5.2); feldspar in clasts (An_89.3±2.3, n=5); matrix feldspar (An_82.5±5.4, n=12).

Classification: (P. McCausland, UWO) Eucrite polymict breccia, moderate shock, low weathering.

Specimens: Type specimens in three fragments totaling 20 g and a polished thin section are on deposit at UWO. Main mass: 118 g, DGregory