Northwest Africa 7514 (NWA 7514)

(Northwest Africa)

Found: Sept 2005

Classification: Rumuruti chondrite (R5)

History: Originally thought not to be a meteorite, and was received by the main mass holder as a gift from a meteorite collector in September 2005. Samples were given to Cascadia in June 2012 and subsequently recognized to be a meteorite.

Physical characteristics: The specimen contains large facets, regmaglypts, and is largely covered by a translucent fusion crust that appears olive gray. In places slight protrusions <1 mm high and ~1-4 mm across are present and covered by crust. A few small broken faces have a brownish weathering patina. A cut face shows a nearly featureless interior with an overall color more gray than that of the fusion crust.

Petrography: (A. Ruzicka and M. Hutson, Cascadia) In thin section the rock shows chondritic texture with a transparent matrix and significant chondrule-matrix integration. Indistinct microporphyritic and barred olivine chondrules are visible; a clast of olivine microporphyry ~4.5 × 3.6 mm across is the largest feature. The rock consists primarily of olivine, with subequal plagioclase and Ca-pyroxene, and accessory chromite, Cl-apatite, pentlandite, and pyrrhotite. Feldspar grain size (length) = 37±18 μm, n=199. Olivine grains show diverse shock characteristics split roughly evenly between stages S2, S3, and S4.

Geochemistry: Phases are generally equilibrated (all values atomic): olivine Fa_38.2±0.5, n=32; plagioclase Ab_84.4±2.0Or_5.7±0.9An_9.9±1.8, n = 20; Ca-pyroxene Wo_40.1±2.5Fs_15.4±1.9, n = 20; chromite [Fe/(Fe+Mg)] = 0.94±0.05, [Cr/(Cr+Al)] = 0.81±0.03, n=14; Ni-rich pentlandite (approximately Fe_0.49Ni_0.51S_1.0) and S-rich pyrrhotite (approximately Fe_0.81 Ni_0.01S_1.0). Oxygen isotope composition: (R. Greenwood, OU) δ¹⁷O = 5.74, δ¹⁸O = 5.04, Δ¹⁷O = 3.12 (all per mil).

Classification: Rumuruti chondrite (R5). Mineralogy, mineral chemistry, and O-isotopic composition consistent with R chondrite group.

Specimens: 40.3 g, two thick slices, and one thin section at Cascadia. Main mass, TStout.