Caleta el Cobre 022        ~24°20’S, ~70°15’W

Antofagasta, Chile

Find: 2016 Nov

Classification: Martian meteorite (Nakhlite)

History: A single stone was found casually by a tourist family next to their night camp in the Atacama desert. The stone was presented to Rodrigo Martinez from MMC, and identified as a meteorite. A sample was then sent by the finder to CEREGE for classification.

Physical characteristics: A single stone entirely covered by shiny fusion crust. Cut surface reveals a dark greenish coarse-grained interior with a few mm-sized orangish crystals. Magnetic susceptibility measured on several pieces is very homogeneous with log χ (× 10^-9 m³/kg) = 3.93±0.01 (N=5, including measurement of the main mass remaining after cutting)

Petrography: Cumulate texture with euhedral elongated augite crystals (typical size 1 mm by 300 μm) with interstitial plagioclase (typical size 250 μm, birefringent) and rare fine grained mesostasis. Olivine crystals (up to 2.5 mm) are crosscut and surrounded by aqueous alteration products ("iddingsite") and contain melt inclusions (to 100 μm). Thin sulfide veins (pyrrhotite) penetrate the olivine crystals. Other notable minerals: finely exsolved Fe-Ti oxides to 1 mm in size, with TiO₂ 16.8 wt% , Cr₂O₃ 2.23 wt%, Al₂O₃ 1.56 wt%, MgO 0.50 wt%, MnO 0.42 wt% (mean of 4 analyses with electron beam defocused to 10 μm). Modal abundances (from image analyses of a 2 cm² polished section): pyroxene 69.0 vol%, plagioclase and mesostatis 27.1 vol%, olivine 2.2 vol%, opaque minerals 1.8 vol%. Magnetic measurements (hysteresis properties of a 360 mg piece) indicate a titanomagnetite content of at least 4.3 wt%. None of the silicates show petrological sign of shock.

Geochemistry: Augite Fs_28.4±2.9Wo_40.0±0.6 (N=20), with Fe-rich ~10 umthick rims (cores down to Fs_24.5, rims up to Fs_33.3), FeO/MnO=37.4±3.6. Plagioclase An_30.4±1.0Ab_66.9±0.8Or_2.8±0.4 (N=7). Olivine Fa_70.2±3.4 (range Fa_67.2-76.4), FeO/MnO=47.6±1.6 (N=7). Olivine alteration products (iddingsite) SiO₂ 53.2 wt%, FeO 26.1 wt%, MgO 2.5 wt%, Al₂O₃ 0.56 wt%, MnO 0.32 wt%, CaO 0.21 wt%, K₂O 0.18 wt%, Na₂O 0.16 wt%, total 83.3 wt% (average of 5 analyses with electron beam defocused at 10 μm). The bulk chondrite-normalized REE pattern (V. Debaille, ULB) is similar to that of nakhlites.

Classification: Martian (nakhlite). Minimal weathering. This nakhlite is unusually rich in plagioclase and in titanomagnetite.

Specimens: 21 g, 3 polished sections, 1 thin polished section at CEREGE. Main mass with anonymous finder