Northwest Africa 4480

Algeria

Find: Summer 2006

Achondrite (Martian, basaltic shergottite)

History: The sample was recovered in Algeria in the summer of 2006. G. Hupé purchased it in Tagounite, Morocco in September 2006.

Physical characteristics: The meteorite is a single, very fresh 13 g ellipsoidal stone, mostly coated by dark brown fusion crust. Maskelynite, yellow-green olivine and tan-colored pyroxene are visible on cut face.

Petrography: (A. Irving and S. Kuehner, UWS) The stone is mostly a relatively fine-grained (mean grainsize 0.15 mm) basaltic rock, but with several coarser grained, glomerocrystic regions.  The dominant matrix consists of plagioclase laths (maskelynite), olivine and complexly-zoned clinopyroxene with accessory Ti-chromite, ilmenite, Mg-Fe-bearing merrillite and rare Si-rich glass or silica polymorph.Glomerocryst regions are composed of coarser (0.5-0.8 mm) plagioclase (maskelynite) and olivine with interstitial pigeonite and ilmenite.

Mineral compositions and geochemistry: Matrix - clinopyroxene is patchily zoned from augite cores (Fs_24.9-31.2Wo_35.3-31.1, FeO/MnO = 30-32) to pigeonite rims (Fs_55.4-56.4Wo_17.5-15.4, FeO/MnO = 36); olivine (Fa_67.9-79.2, FeO/MnO = 49-52); plagioclase (An_58.4-61.0 Or_1.6). Plagioclase in glomerocryst regions is consistently more calcic (An_66.3-68.5Or_0.3). Bulk Composition (R. Korotev, WUSL): INAA of two ~37 mg whole fragments of matrix gave Na 1.40 wt%, Fe 15.8 wt%, and (in ppm) Sc 39.7, Cr 1027, Ni <60, La 1.85, Sm 2.69, Eu 0.86, Tb 1.05, Yb 4.16, Hf 3.16, Th 0.24; the REE pattern shows moderate light REE depletion, elevated heavy REE abundances and a negative Eu anomaly.

Classification: Achondrite (Martian, basaltic shergottite).

Type specimens: A total of 2.6 g of sample is on deposit at UWS. PSF holds the main mass (6.63 g).