Northwest Africa 4908 (NWA 4908)

(Northwest Africa)

Purchased: Prior to 2004

Classification: HED achondrite (Eucrite)

History: Believed by Thompson to have been originally found near Erfoud, Morocco. A portion of the sample was donated to Cascadia on May 3, 2004.

Physical characteristics: The sample is partly covered with a shiny black fusion crust; broken surfaces are gray or have a brown patina that appears to contain brownish-red dust. Cut surfaces show sharply-defined angular to subrounded gray clasts and more diffuse blue-gray clastic areas set in a buff-colored host.

Petrography: (A.Ruzicka and T.J. Schepker, Cascadia) Microscopic inspection reveals the buff areas to be microcrystalline and feldspathic, and the blue-grey areas to be feldspathic and cryptocrystalline to microcrystalline. Larger lithic and mineral clasts (<20% of the sample) are composed mainly of plagioclase and exsolved clinopyroxene, with lithic clasts composed of basalt.

Geochemistry: (A. Ruzicka and T.J. Schepker, Cascadia) Plagioclase has relatively uniform composition (Ab_10.8±0.3An_88.8±0.3Or_0.5±0.1, n = 42) and exsolved pyroxene endmembers include orthopyroxene (Wo_4.2±0.4En_37.1±0.4Fs_58.7±0.4, FeO/MnO = 31.4, n = 21) and augite (Wo_41.1±1.1En_30.3±0.3Fs_28.5±1.0, FeO/MnO = 33.4, n = 5). Oxygen isotopes: (E. Martin and I. Bindeman, UOr) δ¹⁸O = 4.025, δ¹⁷O = 1.931, Δ¹⁷O = -0.183 (mean of two analyses). Replicate analyses of standards suggest ±0.080 per mil error on δ¹⁸O and ±0.027 per mil error on Δ¹⁷O.

Classification: Achondrite (Eucrite), crystalline melt breccia. Weathering is minor.

Specimens: A total of 22 g and 7 thin sections are on deposit at Cascadia. Thompson holds the main mass.