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BRAZIL - PR
Equilibrated Ordinary Chondrite L4.
The meteorite exhibits a well-defined chondritic texture with chondrules varying in size and textures, such as barred, radial and microporphyritic varieties. The edges of the chondrules are well defined within the matrix, which in turn is formed by fine grains with regions still glassy. In the hand sample it was possible to observe that the meteorite contains dark lithic fragments, approximately 5mm in size. Source: Gomes & Keil (1980).
According to Fodor et al. (1977) the meteorite is composed essentially of olivine, pyroxene with low Ca, both varying substantially in composition, and dark fiery glass with some regions with plagioclase. In lesser quantity are the metallic phase FeNi (kamacite and taenite), troilite and chromite with high and low content of Al2O3. As accessory minerals it has pyroxene rich in Ca and nepheline. The lithic fragment has olivine and low Ca-pyroxene, also exhibiting a greater variation in composition, as well as an abundant presence of ferromagnesian silicates, looking like serpentine phases. Glass with heterogeneous composition with some calcium and other sodium grains. Pyroxenes with high Ca and Al2O3 and chromite with low Al2O3 occur in accessory quantities. Source: Gomes & Keil (1980).
Although the chemical composition varies, the olivine and the low Ca-pyroxene of the main mass of the meteorite fit within the chemical L group. An additional support for this classification comes from the composition of the total rock chemistry, with Fe / SiO2 ratios (0.54 ), Feº / Fe (0.31), as well as the total concentration of total Fe in the meteorite (21.40%) and total FeNi of 7.91%. The variety in the composition of ferromagnesian silicates, the well-defined chondrules and the presence of fiery glass in the matrix suggests that the Rio Negro meteorite belongs to the advanced 3 petrographic type, in transition to the 4, according to Van Schmus & Wood (1967). Regarding the origin of the lithic fragment, from its texture, mineral composition and total fragment it seems to be an unequilibrated ordinary and carbonaceous chondrite of the petrographic type 3. However, due to some properties, such as the predominance of Fa40 olivines, suggest a closer relationship to type 3 carbonaceous. The fragment region within the main body of the meteorite leads to the conclusion that the fragment was incorporated into the meteorite by an impact process and that it was once part of the regolith that covered the Negro River. Source: Gomes & Keil (1980).
Not reported by the Meteoritical Bulletin Database. The preliminary description, including some chemical analyzes, was published by Gatterer & Junkes (1940). A more detailed study on the Rio Negro meteorite was carried out by Fodor et al. (1977). Source: Gomes & Keil (1980).
The meteorite fell in the morning (8:30 am local time) on September 22, 1934, at Voltagem, a small farm near Rio Negro. Sound effects were reported by local residents and the meteorite was recovered by Ayres Rouen, former mayor of the city of Rio Negro. Source: Gomes & Keil (1980).
All information that does not have a specific source was extracted from the Meteoritical Bulletin Database.
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