ANGRA DOS REIS

Stony

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CLASSE:

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ACHONDRITE

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BRAZIL - RJ

1869

Fassaite Achondrite. The Angra dos Reis meteorite is an ultramafic igneous rock or pyroxenite because it is made up of 93% pyroxene. Properly referred to as a Fassaite.

PETROGRAFIA:

The meteorite exhibits a granular and recrystallized texture, mainly formed by small xenomorphic fassaite grains with sizes up to 0.5mm (average 0.1mm). Less common are the large poikilitic fassaite crystals that surround the small grains of the matrix. No evidence of stress or shock deformation was observed. Petrographic analyzes show the preferential orientation with a weak lineation in the fassaite matrix and apparently a random orientation for the poikilitic fassaite grains, indicating a cumulative origin for the rock. Source: Gomes & Keil (1980).

GEOQUÍMICA:

The total chemical analysis of Angra dos Reis shows as main characteristics high levels of TiO2 and CaO markedly different from any other meteorite. With the exception of some elements, the abundance of all the rock and fassaite is very similar, reflecting the fact that Angra dos Reis is essentially a pyroxenite rock. The meteorite shows a small negative Eu anomaly, interpreted as due to the recrystallization and removal of plagioclase or as a result of the initial crystallization of melilite, a phase that is speculated to have been removed in the cumulative process. Source: Gomes & Keil (1980).

CLASSIFICAÇÃO:

Angra dos Reis is an ultramafic igneous rock, a pyroxenite composed of 93% pyroxene. This material is slightly pleochroic, varying in color from almost colorless to reddish-brown, with high levels of TiO2 and CaO. It is therefore aptly referred to as fassaite. No evidence of zoning or exsolution was found and its composition is homogeneous, although Hazen and Finger (1977) suggest small variations in composition. Pyroxene analysis is En33.5 Fs11.9 Wo54.6. Prinz et al. (1977b) calculated the analysis based on the following final members: CaMnSi2O6 (0.2%); Ca (Mg0.5Ti0.5) (SiAl) O6 (0.9%); Ca (Fe0.5Ti0.5) (SiAl) O6 (3.2%); CaCr (SiAl) O6 (0.6%) CaAl (SiAl) O6 (15.7%); Ca2Si2O6 (34.1%); Mg2Si2O6 (27.4%) and Fe2Si2O6 (9.7%). A calcium-rich olivine, occasionally containing tiny inclusions of magnesian kirschsteinite, makes up about 5.5% of the meteorite. The accessory phases include spinel, celsian, plagioclase, whitlockite (merrilite), titanium-magnetite, metallic FeNi, troilite, badeleite, SiO2 and terrestrial hydrated iron oxide. The occurrence of doubréelite is doubtful, given the relatively highly oxidized nature of this rock and could not be confirmed by Keil et al. (1976) and Prinz et al. (1977b). Spinel occurs when small, dark green grains are disturbed by the entire meteorite. It is homogeneous and rich in Fe and Al. Celsian is found as a small grain in the meteorite mass. The grains are compositionally homogeneous and contain about 90% of the Celsian molecule. Angra dos Reis is the only meteorite with kirschsteinite and magnesian celsian. Homogeneous and highly calcium plagioclase (An86.0) was found only in separate minerals. Whitlockite (merrilite) is distributed in a non-homogeneous manner, of quite variable size and can represent about 0.3% of the meteorite. The X-ray refinement of its structure indicates that the phase is better known as merrilite. Magnetite forms small, rare grains containing 21.9% TiO2, while metallic FeNi (Fe 95.5, Ni3.5, Co1.5; total 100.15%) is very rare and occurs mainly as small bubbles in troilite (Fe 62.9, Co 0.07, S 36.5; total 99.47%). Based on the total chemical analysis, Ludwig & Tschermark (1887, 1909) calculated 1.26% of troilite for the meteorite, and it appears to be a reasonable value. The minuscule grain of badeleite was recognized by the electron microprobe based on its high Zr content, but it was too small for quantitative analysis. Terrestrial hydrated iron oxide, apparently the result of the weathering of troilite grains, is found as a rare constituent. Source: Gomes & Keil (1980).

CLASSIFICADORES:

There is no information in the Meteoritical Bulletin. The fall was reported and the fragment described by Derby (1888a, b), Ludwig & Tschermak (1887, 1909) and Tschermak (1888). Source: Gomes & Keil (1980).

HISTÓRIA:

The Angra dos Reis meteorite fell around 5:00 am in January 1869 at Praia Grande in Angra dos Reis, in front of the Bonfim Church. The fall was witnessed by Dr. Joaquim Carlos Travassos, who was passing by a boat accompanied by two slaves. The precise date of the fall was not noted, but according to Dr. Travassos it must have occurred in the second half of the month, as it would have been a few days after the birth of a daughter. Two fragments were recovered by the slaves at about two meters deep, and due to the fractures there appeared to be a third fragment, not located, which may still be at the bottom of the sea. The first disclosure on the subject occurred only in 1888 by Derby, who received one of the fragments weighing 446.5 g, which had been donated to Dr. Ermelino Leão, who in turn donated it to the National Museum. From the second fragment, it is only known that he was in the possession of Dr. Travassos' father-in-law (according to research by historian Regina Dantas the father-in-law was called Rogério Antônio de Oliveira, married to Joaquina Rosa de Oliveira). According to Derby, one day this fragment should go to the Museum, however, unfortunately, this prediction never materialized. This meteorite that would weigh between 500g and 1 kg has been lost since then, as it is very common to happen with many Brazilian meteorites, that soon after their falls are kept as priceless precious, but that with time, they fall into oblivion and finally they are lost as scrap or rubble by their own owners or their heirs. Description obtained in the documents of National Museum.

Todas as informações que não possuírem fonte especifica, foram extraídas do Meteoritical Bulletin Database.

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