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BRAZIL - MG
Iron Meteorite - Ungrouped Fine Octahedrite.
The Bocaiúva meteorite has a Widmanstätten pattern with kamacite lamellae dimensions ranging from 0.3 to 0.5 mm. Silicates, for the most part, do not present themselves, morphologically, as isolated crystals. They occur intertwined like links in a chain. The size of the silicates varies, on average, from 1 to 5 mm, although the largest crystal observed was 7.7 mm. The silicate regions are rounded, giving the impression of chondrules. According to Curvello et al. (1985), the silicates correspond to 50mg/g of the meteorite. Plessites of different dimensions and morphologies can also be observed, as well as Newman bands. Schreibersite is adjacent to silicate grains, more precisely olivine, adjacent to troilite and, sometimes, encompassing olivine chondrules (Figure 6). Troilite, on the other hand, is observed encompassed by silicate and also in contact with the kamacite matrix. Eventually, it breaks down into martensitic fields. Source: Pucheta et al. 2011.
Through SEM/EDS analysis, the difference in relief and mineral composition was observed, mainly in relation to silicates and the metallic matrix. The non-opaque minerals identified by chemical spectra correlated to optical microscopy were: forsterite, silicate matrix; rounded pigeonite inside calcium-rich plagioclases and subhedral in olivine; diopside; enstatite; euhedral apatite in contact with kamacite and pentlandite, and calcite. Opaque minerals are: kamacite; taenite, surrounded by olivine; chromite, always trapped in olivine; troilite; schreibersite; goethite, in the contours of the silicates, from terrestrial alteration; magnetite, with vein morphology and agglomerations in olivine, and pentlandite. (Pucheta et al. 2011). The inclusions of forsterite silicate (Fa7.4), enstatite (Fs7.3 En89.6 Wo3.1) and diopside (Fs4.3 En53.9 Wo41.8) in the middle of the metallic phase of kamacite were quite homogeneous, forming a highly balanced mineral assembly (Desnoyers et al. 1985). Metallic phase chemistry, provided by the Meteoritical Bulletin database: 8.49% Ni, 19.5 ppm Ga, 178 ppm Ge and 2.9 ppm In.
According to the Meteoritic Science classification, Bocaiúva does not yet have a classification among researchers in the area, although structurally, and disregarding its silicate regions, it can be classified as a siderite type, belonging to the class of fine octahedrites. However, the most acceptable is to classify it as “metallic silicate”, or ungrouped, that is, it does not fit into any known classification. Source: Pucheta et al. 2011. For more information on the Bocaiúva meteorite, follow the links to the articles cited: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0370-44672011000200004 and http://adsabs.harvard.edu /full/1985Metic..20..113D
Walter da Silva Curvello, Desnoyers et al., (1985), Eustáquio Galvão da Silva, Jacques Danon e John T. Wasson. Source: Dissertation of Flávia Noelia Pucheta (2010).
The Bocaiuva meteorite was scientifically discovered in 1961 according to a manuscript by Professor Walter da Silva Curvello, from the National Museum (MN) of Rio de Janeiro. In 1962 according to Desnoyers et al., (1985) and in 1965 according to the sources found in the Meteoritical Society Bulletin, responsible for the official cataloging of all meteorites found in the world, published in 1984 by Eustáquio Galvão da Silva of the Department of Physics from the Federal University of Minas Gerais (UFMG), Jacques Danon from the Brazilian Center for Physical Research (CBPF) and John T. Wasson from the Institute of Geophysics and Planetary Physics, University of California (UCLA). Source: Dissertation by Flávia Noelia Pucheta (2010). The Bocaiúva meteorite was found by a farmer in the town of Piedade, district of Diamantina (Desnoyers et al., 1985) and taken to the Terra Branca farm, 6 km from the bank of the Jequitinhonha River, also near Diamantina, in the municipality of Bocaiúva. However, it was in 1947 that a group of geologists from the UFMG Radioactive Research Institute (IPR) went to the municipality of Bocaiúva to watch, together with North American researchers, a total eclipse of the sun, and in that episode, found the meteorite propping the door of the farmer's residence. Source: Pucheta et al. 2011.
Todas as informações que não possuírem fonte especifica, foram extraídas do Meteoritical Bulletin Database.
Todas as imagens possuem direitos autorais.
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