San Juan 116 (SJ 116)        25°37.315’S, 69°57.291’W

Antofagasta, Chile

Find: 2019

Classification: Mesosiderite (group C3)

History: Found in the Atacama desert in 2019.

Physical characteristics: An irregular light brown stone without fusion crust.

Petrography: (J. Gattacceca, Bertrand Devouard, CEREGE) Crystalline rock with recrystallized texture. Grain size is about 200 µm, with few larger mineral clasts (to mm). The studied section shows two different lithologies differing mostly by their opaque content. Low-Ca pyroxene is the main mineral, with much lesser amount of olivine. Other minerals: abundant troilite, metal (kamacite and Ni-rich metal, from Fe60Ni40 to Fe45Ni55), chromite. Ilmenite (with TiO₂ and chromite exsolutions) and merrilite (to 100 µm) are also found. No plagioclase was observed. Metal, sulfide and chromite are often euhedral. The lithology with higher opaque has 25.3 vol% troilite 6.8 vol% metal (plus 4.5 vol% of metal weathering products), 5.4 vol% chromite with grain size several hundreds µm (point counting, total counts 221). The lithology with lower opaque content has 10.6 vol% sulfide, 1.7 vol% metal, 0.7 vol% chromite with smaller grain size (30 µm for FeS, lower for metal and chromite) .

Geochemistry: Olivine Fa_29.1±0.7, FeO/MnO = 44.7±5.9 (n=7). Low-Ca pyroxene Fs_26.0±0.3Wo_1.8±0.1, FeO/MnO = 29.5±3.2 (n=12). Chromite Cr# = 0.78±0.01 (n=3). Chromite associated to ilmenite has Cr# ~ 1. Ni-rich metal composition range from Fe60Ni40 to Fe45Ni55 (EDS analyses).

Classification: Achondrite (mesosiderite-C3). Group C based on the absence of plagioclase, metamorphic grade 3 based on the recrystallised texture. This meteorites is particularly rich in tetrataenite.

Specimens: Type specimen at CEREGE. Main mass with ArtMet.