Northwest Africa 4478

Algeria

Find: September 2006

Achondrite (lodranite)

History: G. Hupé purchased the sample in September 2006 in Zagora, Morocco.

Physical characteristics: Two dense, brown stones (298 g and 146 g) lacking fusion crust.

Petrography: (A. Irving and S. Kuehner, UWS) This specimen is composed of large mineral and polycrystalline lithologies (up to 8 mm across) with interstitial fine-grained material of the same phases.The large minerals consist of either olivine or orthopyroxene (with clinopyroxene exsolution lamellae associated with blebs of Ni-free iron metal). The polycrystalline lithology consists mainly of interlocking olivine grains (up to 3 mm across) and sparse large chromite grains with interstitial clinopyroxene, orthopyroxene, kamacite, pyrrhotite, pentlandite and troilite. The modal abundance of metal (+ limonite after primary metal) is 5 vol%. Plagioclase is absent. Olivine grains contain numerous blebby to worm-like polycrystalline inclusions, and clinopyroxene grains contain similar inclusions; some examples exhibit symplectitic intergrowths of these various phases. Some olivine grains contain multiple blade-like lamellae of olivine of a different composition. Narrow elongate zones or discontinuous veinlets of metal are present within clinopyroxene, and adjacent to such metal the pyroxene has a more magnesian composition.

Mineral compositions and geochemistry: Olivine (Fa_10.6-10.9; FeO/MnO = 22.1-23.9), clinopyroxene (Fs_3.9Wo_41.9; FeO/MnO = 10.2), orthopyroxene lamella in clinopyroxene (Fs_9.1Wo_1.3; FeO/MnO = 11.9) and chromite (Cr/(Cr+Al) = 0.822-0.825; Mg/(Mg+Fe) = 0.506 - 0.520, TiO₂ = 0.31-0.37 wt%). Oxygen Isotopes: (D. Rumble, CIW) Quadruplicate analyses by laser fluorination gave, respectively, δ¹⁸O = 2.23, 2.43, 2.23, 2.40; δ¹⁷O = 0.14, 0.30, 0.07, 0.11; Δ¹⁷O = -1.034, -0.984, -1.107, -1.147 (all ‰).

Classification: Achondrite (lodranite).

Type specimens: A total of 20.1 g of sample and one polished thin section are on deposit at UWS. GHupé holds the main mass.