Northwest Africa 8711 (NWA 8711)

Morocco, (Northwest Africa)

Purchased: May 2014

Classification: Ordinary chondrite (L6, melt breccia)

History: Purchased by Nicola Castellano at the Genova Mineral Fair in May 2014 from a Moroccan dealer.

Physical characteristics: Single stone, dark brown crust. A cut surface shows two different areas: angular fragments up to 2 cm of light gray, coarse grained chondritic material and dark-gray, very fine-grained, shock-melted veins up to 2 mm wide intersecting the matrix.

Petrography: (V. Moggi Cecchi) Microprobe examination of a thin polished section displays two distinct domains: the shock-melted domain shows a crystalline portion consisting of ringwoodite, deep blue in plane polars and 20-200 μm wide, plus rare majorite crystals, and a microcrystalline to glassy portion, green in plane polars, made of quenched silicates (mainly augite) with scattered rounded metal and troilite blebs, up to 30 μm wide; the L6 host domain shows an equilibrated chondritic texture with few chondrules not clearly detectable set in a crystalline matrix of olivine, orthopyroxene, minor plagioclase and diopside, Fe-Ni metal, troilite.

Geochemistry: (V. Moggi Cecchi, G. Pratesi, S. Caporali, M. Zoppi, UniFi) Chondritic portion: olivine, Fa_25.1±0.1 (Fe/Mn=48±2, n=8); low-Ca pyroxene, Fs_22.2±0.1Wo_1.4±0.1 (0.18 TiO₂, 0.18 Al₂O₃, 0.13 Cr₂O₃, all wt. %, Fe/Mn=28±2, n=9); diopside, En_8.9±0.0Fs_47.0±0.3Wo_44.3±0.3 (0.40 TiO₂, 0.50 Al₂O₃, 0.88 Cr₂O₃, 0.29 MnO, 0.54 Na₂O, all wt. %); ringwoodite, Fa_27.8±0.7 (Fe/Mn=182±3, n=10); majorite, Fs_21.3±0.3Wo_1.2±0.1 (Fe/Mn=27±2, n=11). Shock melt (broad beam electron microprobe): 47.59 SiO₂, 27.17 MgO, 16.64 FeO, 2.60 CaO, 3.19 Al₂O₃, 0.38 MnO, 0.10 TiO₂, 0.33 Cr₂O₃, 1.20 Na₂O, 0.13 K₂O, 0.17 NiO, all wt. %, n=7.

Classification: L6-melt breccia, W2, S5

Specimens: 21.2 g and one PTS are on deposit at MSP, Nicola Castellano holds the main mass.