BRAZIL - PA
Equilibrated Ordinary Chondrite H5 with moderate shock stage S3.
The Ipitinga chondrite consists of a single polyhedral stone, covered with crust. Terrestrial weathering is evident from its light brown outer surface and the presence of limonite in its inner portion. Optical investigation shows that the meteorite has a chondritic texture, with different types of chondrules (porphyritic, granular, barred, radial and remains of chondrules). The chondrules are generally rounded, make up about 30-40% of the meteorite and vary from 0.2 to 3 mm in size. However, they have poorly outlined contours, defined in a fine-grained recrystallized matrix. Source: Dreher et al. (1995).
Mineralogical and electron microprobe studies reveal that the meteorite mainly contains olivine Fa18.3 and orthopyroxene Fs16.2Wo1.3 of fairly uniform compositions, with smaller amounts of FeNi metal (kamacite, taenite and plessite), troilite, Cr-diopside (En48. 1 Fs5 .3 Wo46.6) and plagioclase (An13.6 Ab80.1 Or6.3). Chromite, magnetite and limonite are accessory minerals, with the latter two occurring mainly as metal alteration products (weathering). Source: Dreher et al. (1995).
The Ipitinga meteorite is classified as a group H chondrite based on the composition of its minerals, particularly those of olivine and orthopyroxene, in addition to plagioclase and chromite. A group H classification is also confirmed by some mass chemical analyzes, which indicate Fe / SiO2 (0.78) and total Fe (27.17%). Based on the uniform compositions of olivine and pyroxene, the strong recrystallization of the matrix, the microgranoblastic and fibrous texture in many canal mesostases and the contours of poorly outlined chondrites, Ipitinga is placed in the petrological class 5 of Van Schmus & wood (1967). Also consistent with this classification are the low average CaO content of olivine (0.01%), considered typical of equilibrated chondrites by Dodd (1972) and the average Wo content of orthopyroxene (1.3 mol%), which is within the range of Wo 1.2-1.6 for class 5 petrological meteorites, given by Scott et al. (1986). Additional characteristics, such as the presence of weak undulating extinction and planar fractures in olivine, as well as the occasionally deformed aspect of plagioclase, indicate that the meteorite is slightly modified by a shock event, belonging to stage S3 by Stoffler et al. (1991). For more information, the link to access the source is http://rigeo.cprm.gov.br/jspui/handle/doc/532. Source: Dreher et al. (1995).
Dreher, A. M. and Dall'Agnol, R.
Ipitinga was found by geologist S.L.Martini in March 1989 during routine fieldwork, approximately 1km from the Treze de Maio district and 15km southwest of the Serra de Ipitinga, in a concession area of Transamazônica mining Ltda. in the state of Pará. It was recognized as a meteorite in July of the same year, having been the first meteorite found in the Brazilian Amazon region. It is a single mass of approximately 7 kg and a polyhedral shape (20 x 14 x 14 cm) giving the clear impression that the meteorite has fragmented in the air with other samples not found in the same region. The meteorite was in a corner of the road and caught the attention of its discoverer because it stands out a lot from the lateritic terrain of the region. The meteorite was slightly altered by weathering and possibly reached that location during the implementation of the road. Source: Dreher et al. (1995).
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