El Médano 200        ~24°51’S, ~70°32’W

Antofagasta, Chile

Found: 2011 Oct 29

Classification: C3

History: A single stone was found in the Atacama desert by Pierre Rochette in October 2011.

Physical characteristics: A single 2.4 g stone with fusion crust. The interior is uniformly dark and porous.

Petrography: (J. Gattacceca, CEREGE) The meteorite consists of small chondrules (mostly type I, often with a fine-grained dark rim), chondrule fragments, mineral fragments (up to one mm) in a fine-grained matrix. Modal abundances: matrix 55%, chondrules and mineral fragments 45%. Chondrule mean size is 130±80 μm (N=41). Some chondrules show Fe diffusion rims in the olivine (~2 μm thick). Presence of dusty olivine. Abundant assemblages of magnetite and sulfides (troilite) up to 100 μm. Rare metal. Based on magnetic measurements, magnetite content is estimated to ~19 wt.% under the form of fine grains in the matrix. Powder XRD pattern lacks phyllosilicate reflections. Raman spectra of the matrix (L. Bonal, IPAG) suggest minimal thermal metamorphism. IR spectra of the matrix (L. Bonal, IPAG) suggest some aqueous alteration and the presence of carbonates.

Geochemistry: Olivine Fa_0.3-69.5 (mean 22.7±23.6, PMD Fa = 94%, N=39). Cr₂O₃ in ferroan olivine is 0.36±0.24 wt.% (N=30). Orthopyroxene Fs_1.6±0.5Wo_0.7±0.4 (N=7). Ca-rich pyroxene Fs_1.5-17.4Wo_42.3-28.1 (N=3). Three metal analyses give Fe46.5±3.5Ni53.5±2.3 indicating Ni-rich taenite or tetrataenite. Oxygen isotopic compositions: (J. Gattacceca and C. Sonzogni, CEREGE) analysis of a 1.5 mg acid-washed sample by laser fluorination gave δ¹⁷O = -5.15, δ¹⁸O = -1.74, Δ¹⁷O = -4.25 (all per mil). Mag susceptibility log χ =5.08 (χ in 10^-9 m³/kg).

Classification: C3 with affinities to CO3.

Specimens: One gram and a polished section at CEREGE. Main mass with CEREGE.