Northwest Africa 2999

Morocco or Algeria

Find: 2004

Achondrite (angrite)

History: Twelve individual dark brown stones totaling392 g, each with a thin fusion crust, were purchased from a Moroccan dealer inTagounite by G. Hupé in August 2004.

Physical Characteristics: Grain size is predominantlyfrom 0.1 to 0.5 mm, but all stones have irregularly distributed, largeryellowish plagioclase grains (up to 6 mm across) exhibiting an iridescentluster.

Petrography: (A. Irving and S. Kuehner, UWS;T. Bunch and J. Wittke, NAU) Based upon examination of thin sections ofall separate stones, this meteorite is texturally heterogeneous. Terrestrialweathering has resulted in partial replacement of metal and minor grainboundary staining by iron hydroxides. The overall texture is protogranular, butthere are large porphyroclasts of anorthite, spinel, and polygranular olivine.Anorthite also occurs as narrow (10–20 µm wide) coronas around spinel grainsadjacent to clinopyroxene and both spinel and diopside are compositionallyzoned away from the coronas. Texturally, this meteorite is very different frommost angrites.

Geochemistry: The major minerals are Ca-rich olivine(Fa_39.8–41.0; FeO/MnO = 77–97; CaO = 0.6–1.3 wt%), Al,Ti-bearingdiopside (Fs_9.6–11.3Wo_53–54; FeO/MnO = 55–130; Al₂O₃= 5–9, TiO₂ = 0.5–2.4 [both wt%]), minor Cr-pleonaste spinel(Mg/(Mg+Fe) = 0.44–0.47, Al₂O₃ = 55–60, Cr₂O₃= 4.7–8.7 [both wt%]), pure anorthite (containing Na₂O < 0.02wt%), and kamacite, troilite, and S-bearing calcium silicophosphate. Oxygenisotopes: (D. Rumble, CIW) Triplicate analyses of acid-washed whole rocksamples by laser fluorination gave, respectively, δ¹⁸O = 3.839,4.093, 4.154; δ¹⁷O = 1.974, 2.054, 2.095; ∆¹⁷O= −0.041, −0.095, −0.086 (all ‰).

Classification: Achondrite (angrite).

Specimens: A 22 g type specimen and one polished thinsection are on deposit at NAU*. Three polished thin sections are on depositat UWS. GHupé holds the main mass.