Northwest Africa 4735

Erfoud, Morocco

Find: 2003

Primitive achondrite (acapulcoite/lodranite)

History: Bought in Erfoud in 2003.

Physical characteristics: One single stone of 64 g, prismatic shaped, about 2 × 1.5 × 5 cm. The thin dark brown fusion crust is rather fresh. Discrete, millimeter-sized regmaglypts are visible. One surface is broken.

Petrography: (A. Jambon, O. Boudouma and D. Badia. UPVI) Study of a polished section of 1 cm2 reveals the rock is composed mostly of mm-sized low Ca pyroxene. Interstitial metal patches from 0.1 up to 1 mm are observed (kamacite sometimes enriched in Ni due to secondary oxidation). Most are rimmed by iron oxide. Iron sulfide may or may not be associated with metal. Olivine crystals may be as large as low Ca pyroxene mostly altered and replaced by clay minerals. Plagioclase and diopsidic pyroxene are subsidiary smaller interstitial phases. Some μm-sized rounded clinopyroxene crystals are poikilitically enclosed in plagioclase. The texture is equilibrated granulitic. Thin irregular fractures are filled with iron oxides. Mode (vol%): Low-Ca pyroxene 50.4, olivine and its alteration products about 5–10, diopsidic pyroxene 6.0, plagioclase 6.6, kamacite 17 (4.2 metal plus 8.8 oxidized), chromite 4, troilite 8.1, voids 1.3. Minor serpentine and chlorite.

Geochemistry: Olivine Fa₁₀. Low-Ca pyroxene En₉₁Fs₈Wo₁. Diopside: En₅₀Fs₄Wo₄₆ with 1.1 wt% Cr₂O₃. Chromite (Cr₂O₃ = 62.6%, Al₂O₃ = 5.7%, MgO = 9.3%, MnO = 2.6%, FeO = 15.8, TiO₂ = 0.9%) kamacite (Ni = 7.0%; Co/Ni = 0.063). Feldspar Ab₈₁An₁₂Or₇. Logχ (nm³/kg): 5.6.

Classification: Primitive achondrite (acapulcoite-lodranite) According to grain size this rock could be classified as a lodranite; according to its opx/olivine ratio it could be considered as an acapulcoite.

Type specimens: A total of 12.2 g and one polished section are on deposit at UPVI. Moroccan Import (Asnières, France) holds the main mass.