Northwest Africa 1827

Morocco

Purchased 2003 June

Mesosiderite

A complete stony-iron meteorite (877 g) was purchased in Rissani by a Moroccan dealer for N. Oakes (Oakes) in 2003 June.  Classification and mineralogy (A. Irving and S. Kuehner, UWS and T. Bunch, NAU): Igneous texture, mostly medium-grained but with some large mineral clasts of orthopyroxene and plagioclase (commonly surrounded by metal-rich areas).  Predominantly orthopyroxene with about 10 vol% metal (5 wt% Ni), troilite, chromite, merrillite, and sparse, large anorthite clasts (An_90.5Ab₉₁Or_0.4 to An_95.1Ab_4.6Or_0.2).  Large orthopyroxene clasts are more magnesian (Fs_16.2Wo_0.8, FeO/MnO = 34.8) than the predominant medium-sized orthopyroxene grains (Fs_22.5Wo_2.1 to Fs_27.3Wo_2.2, FeO/MnO = 29.7-32.7).  Small elongate grains of a secondary Ca-Fe-rich phosphate mineral occur along fractures in merrillite grains, and probably are of terrestrial origin.  Although this sample resembles a “metal-rich diogenite” rather than a mesosiderite, comparative studies by T. Bunch (NAU) of this sample, NWA 1879 and similar material provided by A. Jambon (UPVI) and M. Farmer have demonstrated that all (with an estimated total weight of over 22 kg) are part of a large, heterogenous mesosiderite (tentatively assigned to class C) containing sparse eucritic and diogenitic clasts (Bunch et al., 2004).  Specimens: type specimen, 20 g, UWS, 1 g and one polished thin section, NAU; main mass, Oakes.