Northwest Africa 14608 (NWA 14608)

Adrar, Mauritania

Find: 2014

Classification: Ordinary chondrite (L, melt breccia)

History: Edwin Thompson purchased from Mohamed Alkhalil, who said that 5 stones with a total mass of 10 kg were found in 2014 near the village of Chinguetti, in Adrar district, northern Mauritania. A 179.7 g end piece from one stone was donated to Cascadia.

Physical characteristics: Physical Characteristics: A glossy, dark weathered surface covers three sides of the sample donated to Cascadia. A single light colored chondrule 0.5 cm in diameter, and numerous protruding bumps of metal are visible on the exterior. The fourth side is a broken surface, which is the same dark gray as the exterior. A thin coating of reddish-brown patina covers approximately one-fourth of the broken surface. Smaller light colored chondrules can be seen on the broken surface, along with pits and small grains of metal/sulfide. A small corner was cut from the sample. The cut face contains a large (1.5 × 0.2 cm) discontinuous metal/sulfide vein, and numerous small (≤ 0.5 mm across) grains of metal. Approximately 5 % of the cut face is covered by vugs ≤ 0.5 mm across.

Petrography: (M. Hutson, A. Ruzicka, Cascadia): Abundant chondrules and chondrule fragments can be discerned in thin section; three large chondrules (1.5-2 mm diameter) contain irregularly-shaped light-colored interiors with black rims from which "fingers" extend into the interior. In reflected light, it can be seen that the black rims contain numerous very fine inclusions of sulfide. Small patches of inclusion-filled brown glass can be seen both between chondrules and in chondrule interiors. Most of the silicates in the section contain networks of small sulfide and metal grains. A large discontinuous vein composed predominantly of metal cuts partway across the section. Larger metal grains have scalloped edges and are often surrounded by troilite. Larger troilite grains are polycrystalline and many contain numerous silicate inclusions. Numerous large Cr-spinel grains (up to 150 µm across), many containing sulfide inclusions, are also present. BSE images show that interchondrule areas contain a mix of inclusion-poor feldspathic material that appears to have been fluidized and glassy, and a fine-grained (≤2 µm) assemblage of pyroxene, olivine, metal and sulfide set amidst feldspathic glass. Numerous vugs occur in the feldspathic patches. A single round object comprised of feldspathic material and Cr-spinel grains is present in thin section; the center of this object contains a small patch of inclusion-filled glass.

Geochemistry: Olivine Fa_23.8±0.6, N=34; Low-Ca pyroxene Fs_20.1±0.4Wo_1.8±0.6, N=28; High-Ca pyroxene Fs_8.7±0.7Wo_42.1±1.5, N=6. Feldspathic material from five areas selected randomly across the section is fairly equilibrated: Ab_80.9±0.8Or_6.4±0.7, N=13; feldspathic material from the single chromite-feldspathic object is not equilibrated: Ab_69.8±8.7Or_4.5±1.6, N=11. Cr-spinel grains within the Cr-spinel-feldspathic object are also not equilibrated, with molar Cr# = 7.59 ± 8.9 Fe# = 76.0±3.0, N=6. Cr-spinel grains selected randomly across the section are equilibrated in Cr/(Cr + Al), with molar Cr# = 85.7±0.4 and Fe# = 73.0±1.7, N=8.

Classification: L-melt breccia based on mineral composition and texture.

Specimens: Cascadia holds 170.0 g in one piece, as well as a polished thin section and material in a potted butt; Thompson holds the main mass.