Northwest Africa 13857 (NWA 13857)

Algeria

Purchased: 2020

Classification: Achondrite (ungrouped)

History: Fabien Kuntz purchased the 475.9 g sample from a meteorite prospector in Tindouf, Algeria, in 2020.

Physical characteristics: The exterior is dark-brownish orange and irregular shaped. The interior is weathered, dark-brown and has a crystalline texture.

Petrography: Description and classification (A. Love, App) Sample shows poikilitic texture composed of (vol%): 2mm (n=15) orthorhombic pyroxene oikocrysts (31), 114µm (n=46), yellow to brown stained, subhedral-euhedral olivine (52) occurring as chadacrysts and phenocrysts. Some pyroxenes are lath-shaped have rims of Ca-rich pyroxene. These phases are set within a vesicular, high-Si (~70wt% SiO₂) glass containing rounded FeS and euhedral chromite. Chondrules are absent. Additional minerals are: rounded blebs of troilite, chromite, apatite, FeOH. Sample vestiges or relict chondritic-textured lithologies; evidence of rapid growth textures (cellular metal-sulfide mixtures, or spherical metal droplets).

Geochemistry: Olivine (Fa_25.9±1.5, Fe/Mn=45.1±1.7, n=14); low-Ca Pyroxene (Fs_18.2±0.9Wo_2.3±1.1, Fe/Mn=29.7±1.7, n=5); high-Ca pyroxene (Fs_15.0±1.2Wo_30.7±2.9, Fe/Mn=23.3±2.8, n=7); glass (wt%: Na₂O=3.6; Al₂O₃=19.6; SiO₂=71.0; K₂O=0.92; CaO=3.3; FeO=1.4). Oxygen Isotopes: (K. Ziegler, UNM) analyses of acid-washed subsamples by laser fluorination gave (all per mill): δ¹⁷O=3.917, 3.730; δ¹⁸O=5.590, 5.095; Δ¹⁷O=0.966, 1.040.

Classification: Achondrite (ungrouped) strong shock, moderate weathering. Sample shows igneous texture, pyroxenes with compositional zoning and has mineralogic and isotopic similarities to L ordinary chondrites.

Specimens: Fabien Kuntz holds the main mass. Three fragments weighing 34.04 g and a polished thin section are on deposit at App.