IBITIRA

Stony

TIPO:

CLASSE:

CLAN:

GRUPO:

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TIPO PET.:

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PAÍS:

ANO:

DESCRIÇÃO:

ACHONDRITE

VESTA

HED

EUCRITE

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-

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BRAZIL - MG

1957

Monomithic eucrite of non-brecciated pigeonite-augite from the asteroid Vesta.

PETROGRAFIA:

The most striking textural characteristic of the meteorite is the presence of vesicles, almost spherical and very uniform in size, comprising about 5 to 7% the volume of the meteoritic rock. The meteorite is holocrystalline, with fine grains and exhibits a pronounced hornfelic texture. No evidence of breccias in the studied samples. However, textural and mineralogical evidence indicates that the meteorite was submitted to a high metamorphism by shock, in which it affected the plagioclase present, the tridymite. The meteorite's surface is covered by a melting crust. Source: Gomes & Keil (1980).

GEOQUÍMICA:

According to Wilkening & Anders (1975) and Steele & Smith (1976a, b), the meteorite essentially consists of pyroxene (60% vol.) And plagioclase (30% vol.), With smaller amounts of tridimite (5% vol. ) and accessory minerals such as olivine, chromite, ilmenite, FeNi metal (kamacite), troilite and merrillite totaling the other 5% of the rock volume. The pyroxene present is mainly pigeonite (En39.0 Fs57.3 Wo3.7) with augite lamellae (En31.4 Fs26.7 Wo41.9) well defined in most grains. Plagioclase is non-zoned and exhibits mosaicism during extinction and variable structural states. Its composition is constant with an average of An95. Fe-olivine (Fa83.3) is found surrounding of an agglomerate of ilmenite- Ti-chromite, where ilmenite and chromite are the main opaques present. They are intergrown with each other and have a uniform composition in each intergrowth, although the latter show considerable variation between them. Grains chosen from the vesicle have the same composition. Kamacite is generally associated with troilite, but troilite can also occur in isolated grains. Troilite can also be associated with chromite-ilmenite or surrounding the pyroxene grains. Steele & Smith (1976b) data shows different concentrations of Co and Ni in the FeNi phases, depending on the nature of the mineral association. When associated with troilite, Co ranges from 0.80 to 1.10% and Ni (~ 0.88%). When FeNi is associated with opaque phases, these concentrations are lower (Co 0.40-0.60%; Ni 0.10-0.35%). Source: Gomes & Keil (1980).

CLASSIFICAÇÃO:

Ibitira is a eucrite of the clan known as HED, originating from the asteroid Vesta, and one of the few monomithic achondrites of non-brecciated pigeonite-augite, despite showing evidence of a high shock metamorphism, giving the meteorite a recrystallized characteristic. Source: Gomes & Keil (1980).

CLASSIFICADORES:

There is no record in the Meteoritical Bulletin. The fall was reported by Menezes (1957) and the meteorite was listed by Hey (1966) and Hutchison et al. (1977). Source: Gomes & Keil (1980).

HISTÓRIA:

It fell on June 30, 1957, around 17:00 on the Monjolo farm, in Martinho Campos, near Ibitira. The meteorite was only recovered because an amateur astronomer watched the fall and the César Lattes Center for Astronomical Studies (now CEAMIG, located at Colégio Santo Agostinho in Belo Horizonte), sent letters to all city halls in the region asking the direction in which the bolide went . All kinds of evidence indicated the end point of the trajectory for the Martinho Campos area, near the village of Ibitira, with only about 200 inhabitants at the time. At Fazenda Monjolo, near Ibitira, the sound of thunder was followed by a whistle like the passing of a bullet, immediately followed by the sound of something falling on the ground, a boy in the region heard the noise and saw the cattle running from the pasture over the hill into the valley. The search carried out by observers at the center, in the hunt for fragments of the meteorite, was unsuccessful, given that the place of fall is a difficult savannah to investigate. So they returned to Belo-Horizonte, where they organized a caravan for the search, which can only continue on the 3rd August. When they returned to Ibitira, they were informed that a farmer, while gathering firewood in capoeira, had found a strange stone that he had picked up and given to the local pharmacist. It was a meteorite of about 2.5 kg with a shiny black outer layer typical of some types of achondrites, although the internal vesicular structure differed from all meteorites known until then. The analysis was carried out by the Technological Institute of Belo Horizonte, which despite having given the petrological description, did not classify it as a meteorite. The publication and recognition was given in December 1957 in the Meteoritical Bulletin nº 6. Description obtained in the documents of M. E. Zucolotto.

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

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