Northwest Africa 4833

Northwest Africa

Find: 2007

Achondrite (lodranite)

History and physical characteristics: A 608 g dark stone with a dull desert varnish and no remaining fusion crust was found in northwest Africa in 2007 and purchased by A. Aaronson in July 2007.

Petrography: (T. Bunch and J. Wittke, NAU) The stone displays a coarse-grained (olivine grains up to 6 mm) hypidiomorphic texture. Orthopyroxene shows a common lobate grain boundary relationship with olivine. Orthopyroxene is highly decorated with exsolved linear to bleb-shaped diopside (0.002 to 0.04 mm in size) that is oriented parallel to at least three crystal planes of the orthopyroxene host. Olivine is decorated with 0.005– 0.02 mm sized ovoid-shaped microlites of plumose chromite set in anhedral diopside. Mineral modes (vol%) are: olivine = 65, orthopyroxene = 30, metal and oxidized metal = 2, chromite and diopside = 3, no plagioclase was found. The shock level is S3 based on moderate mosaic extinction in olivine and orthopyroxene and minor shock twinning in both.

Mineral compositions: Olivine (Fa_10.1; FeO/MnO = 23), orthopyroxene (Fs_9.4Wo_2.3; FeO/MnO = 14), diopside (Fs_8.0Wo_45.9; FeO/MnO = 11), metal (2.98 wt% Ni) and FeS Cr = 1.1 wt%. Chromite cr# = 85.

Classification: Achondrite (lodranite).

Type specimen: A 22.2 g sample is on deposit at NAU. A. Aaronson holds the main mass.