The Palmas de Monte Alto meteorite: mineral chemistry and petrographic features
DOI:
https://doi.org/10.11606/issn.2316-9095.v18-132539Keywords:
Meteorite, Iron, Nickel, Palmas de Monte AltoAbstract
Several parameters have been used to classify iron meteorites, mainly mineralogy and chemical and structural properties. This paper presents these classificatory parameters, allowing a more detailed view to enlarge knowledge about the Palmas de Monte Alto meteorite. This siderite was found on the top of Monte Alto ridge, before 1955, being one of the six specimens that compose the Bahia State meteorite collection. It consists of a single mass of 97 kg which shows a highstage of oxidation in places where the crust has been removed. Its mineralogy includes kamacite, taenite, plessite, as well as secondary mineral phases such the Fe-Ni oxide akaganeite. There are also accessory minerals of common occurrence in Fe-Ni alloys of spatial origin like schreibersite, chromite and troilite, and a rare solid solution of Fe-Mn orthophosphates composed by the minerals heterosite-purpurite or sarcopside-graftonite as extreme members. The average width of its bands of kamacita (0.95 ± 0.15 mm) allows classifying it structurally as a medium octahedrite, with a medium and well-defined Windmasttaten pattern. Its contents of Ni (9.40 wt %) and Co (0.46 wt %) — compared to trace-elements Ga (22 ppm), Ir (0.70 ppm), As (16.00 ppm) and Au (1.70 ppm) — recommend the inclusion of this meteorite in the chemical group IIIAB.
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