Northwest Africa 4748

Northwest Africa

Find: 2005

Achondrite (eucrite, polymict)

History: The meteorite was bought by the main mass holder from a Moroccan dealer during the Munich Mineral Fair, Germany, 2005. The exact find location is not known.

Physical characteristics: Single oval stone of 80 g with a partly weathered shiny black fusion crust. The half of the stone that was wedged in the ground is covered with carbonate.

Petrography: (J. Schlüter, Hamb) Breccia, rich in mineral fragments with few lithic fragments. Rich in troilite and metal with metal grains up to 2 mm in size. Troilite occurs finely dispersed throughout the meteorite, attached to metal grains and frequently as symplectitic intergrowths with clinopyroxene (up to 400 μm in size). The main silicate phases are calcic plagioclase and clinopyroxene (pigeonite), which shows fine exsolution lamellae. Microprobe analyses of such grains give intermediate values. Further subordinate to rare components are chromite, orthopyroxene, olivine and silica.

Geochemistry: Plagioclase (n = 18) An_94.09Ab_5.79Or_0.12, pigeonite (n = 13) Fs_44.49En_53.23Wo_2.28. Several further clinopyroxene grains with differing chemistry (higher Wo or lower Fs). Orthopyroxene (n = 2) Fs_26.62En_70.63Wo_2.75. Olivine in a lithic fragment (n = 2) Fa_33.60. Metal with 5.09 wt% Ni (n = 3) and 40.15 wt% Ni (n = 1).

Classification: Achondrite, brecciated (eucrite, polymict). Appears to have a low degree of shock and minor weathering.

Type specimens: A 17 g sample and one polished thin section are on deposit at Hamb. Wuthenau, holds the main mass.