Heavily weathered primitive achondrite found during the 2nd Meteorite Recon expedition in the Bir Aridal DCA. This specimen represents one of only 38 brachinites known worldwide (as of 2015), and the only documented find of this classification in Africa.
History: Found by Svend Buhl and Tomas Fuellengraben on April 24, 2013
Physical characteristics: A single brownish, oxidized stone.
Petrography: Optical microscope examination of a polished section reveals an equilibrated texture with triple junctions. Main mineral is olivine (grain size 400 μm). Accessory plagioclase (grain size 500 μm) and pyroxene (grain size 150-400 μm). Presence of Ca-phosphate and chromite.
Geochemistry: Olivine Fa=28.6±0.7 (n=14), FeO/MnO=50.0±1.8; Augite Fs=10.6±0.2 (n=3) Wo=43.7±0.2 (n=3), FeO/MnO=28.0±2.1, Al2O3=0.6 wt%; Plagioclase Ab82.2 O1.4 An16.34. Oxygen isotopic composition (J. Gattacceca, C. Sonzogni, CEREGE) δ17O=3.10 per mil, δ18O=6.17 per mil, Δ17O=-0.11 per mil (analysis of 1.5 mg of hand-picked olivine grains after acid washing of a 200 mg powdered sample, TFL slope=0.52).
Classification: Based on petrography, geochemistry and oxygen isotopic composition this is a primitive achondrite (brachinite).
Specimens: 26 g at FSAC, 14 g at CEREGE. Main mass with Svend Buhl.
November 1, 2015
Achondrites, Finds, Stones