Caleta el Cobre 022 (Nakhlite)

Caleta el Cobre 022 (Nakhlite) has been registered in the Meteoritical Bulletin Database

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Caleta el Cobre 022 (Nakhlite) with cut surface revealing typical Nakhlite matrix (30 November 2016). Photo: Rodrigo Martinez

Another photo of Caleta el Cobre 022 (Photo: Jérôme Gattacceca)

“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 Fs28.4±2.9Wo40.0±0.6 (N=20), with Fe-rich ~10 umthick rims (cores down to Fs24.5, rims up to Fs33.3), FeO/MnO=37.4±3.6. Plagioclase An30.4±1.0Ab66.9±0.8Or2.8±0.4 (N=7). Olivine Fa70.2±3.4 (range Fa67.2-76.4), 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”