Northwest Africa 1460

Morocco

Find: June 2002

Achondrite (Martian, basaltic shergottite)

History: In January 2002, A. Habibi provided several small fragments of a 70.2 g complete stone with a fresh, black fusion crust to A. and G. Hupé for analysis. N. Oakes later purchased the stone for more detailed investigation.

Physical Characteristics: A complete stone weighing 70.2 g with a fresh black fusion crust. Dimensions of the stone are 47 × 34 × 27 mm.

Petrography: (A. Irving and S. Kuehner, UWS) The stone is largely unweathered and coarse-grained, with large, pale yellow-green pyroxene and glassy maskelynite laths clearly visible. Texture is subophitic to intersertal.

Geochemistry: Pyroxenes are zoned with cores of orthopyroxene (Fs₂₀Wo₃; FeO/MnO = 30.7) mantled by augite (Fs₂₇Wo₃₁; FeO/MnO = 32.2) with rims of Fe-rich pigeonite (Fs₅₅Wo₁₈ to Fs₈₅Wo₁₃; FeO/MnO = 41.0–36.8). Plagioclase (Ab₅₁Or_1–2, maskelynite) has patchy compositional zoning. Accessory minerals are merrillite, Cl-F-bearing apatite, exsolved Fe-Ti oxides (ilmenite lamellae in titanomagnetite), ilmenite, chromite, pyrrhotite, K-rich glass, silica, and baddeleyite (occurs as blades up to 50 µm long). Fine-grained symplectitic intergrowths composed of fayalite+silica+hedenbergite occurs at the margins of pigeonite grains. Other symplectitic intergrowths of fayalite+silica also occur, commonly at the boundaries between merrillite and pyroxene. Textures, mineralogy, and mineral compositions are essentially identical to NWA 480, with which this sample is paired. Cosmogenic isotopes: (K. Nishiizumi, SSL) Give a cosmic ray exposure age of 2.6 ± 0.2 Ma. Radiogenic isotopes and formation age: (L. Nyquist and C.-Y. Shih, JSC) A preliminary Sm-Nd isochron age of 352 ± 30 Ma and a Rb-Sr isochron age of 313 ± 3 Ma.

Classification: Achondrite (Martian, basaltic shergottite); minimal weathering.

Specimens: A 2.5 g type specimen is on deposit at JSC. A 2.6 g type specimen and one polished thin section are on deposit at MNB. A 5.7 g type specimen and two polished thin sections are on deposit at UWS. A 3.5 g type specimen is on deposit at NAU. An anonymous collector holds the main mass.