Northwest Africa 4742

Morocco

Find: 2001

Achondrite (polymict ureilite)

History: This meteorite was purchased from nomads in Erfoud and acquired by MNHN in 2007.

Physical characteristics: The meteorite comprises a single stone, light tan in color, with altered fusion crust and prominent crystals. It also contains numerous bright crystallites (diamonds). A one-cm splinter on one edge is covered with some thin desert varnish. The total mass of the stone is 376 g.

Petrography: (M. Denise, MNHNP Paris; A. Jambon, O. Boudouma, D. Badia, UPVI; C. Le Guillou and J-N Rouzaud, ENSParis) Classification by EMPA, SEM, and Raman spectroscopy is based on examination of one polished section. The sample contains abundant mm-sized clasts (~30 vol%) of olivine with Fo-rich rims. Within the clasts, reduction rims extend over about 50 μm. The clasts are surrounded by a matrix composed of olivine, low-Ca pyroxene, and subsidiary augite of typically 20–30 μm with a mosaic texture. Numerous mm-sized, interconnected clusters of carbon infill fractures in the matrix. Carbon (~3.5 vol%) is partly amorphous, mostly polycrystalline aggregates of diamond and lonsdaleite (TEM, Raman, XRD) up to several mm and is found in systematic association with oxidized iron sulfide and metal. The thin section also shows rare Ca-carbonate filled veins.

Mineral compositions and geochemistry: Olivine clasts (core) Fo₇₉; Cr₂O₃ 0.6%, CaO 0.3%; FeO/MnO = 44; rims and interstitial olivine up to Fo₉₆. Abundant low-Ca pyroxene: En₈₄Fs1₅Wo₁; FeO/MnO = 42. Minor high-Ca pyroxene variable up to: En₄₅Fs₁₀Wo₄₅; FeO/MnO = 29, Mg# 75 to 81. Remnants of kamacite with 2% Ni are usually altered. Oxygen isotopes (R. Greenwood and I. Franchi, OU) δ¹⁷O = 4.71‰, δ¹⁸O = 9.61‰, Δ¹⁷O = -0.29‰.

Classification: Polymict ureilite

Type specimens: A specimen of 32 g and one polished section are on deposit at UPVI. MNHNP Paris holds the main mass. 10 g Moroccan Imports, Asnières, France