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MAFRA
Stony
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CHONDRITE
ORDINARY
H-L-LL
L
3-4
-
-
BRAZIL - SC
1941
Slightly Equilibrated Ordinary Chondrite L3-4. It presents petrographic type clasts 4-5, being a genomic breccia, with evidence of having suffered shock events.
PETROGRAPHY:
The meteorite exhibits a well-defined chondritic texture with chondrules ranging from subangular to subcircular and a very varied internal texture (barred, porphyritic, radial, etc.). Some chondrite appear to have been implanted while still partially fused, as they have adapted to the adjacent chondrules. The matrix of the chondrules is cloudy and, in some cases, is burgundy color. Small crystals (1-5 micrometers) are commonly present in this cloudy glass. The meteorite matrix is crystalline, but fine-grained. The meteorite also contains many lithic clasts that, in general, have a texture similar to the rest of the rock. The boundaries of clasts are generally sharp and distinct. Some clasts show clear evidence of being moderately shocked, as indicated by the wave extinction of some minerals and the presence of black veins from shock events. Source: Gomes & Keil (1980).
GEOCHEMISTRY:
Melfi (1965) showed that silica and metallic fractions are approximately 69% and 31% in volume of the entire rock, respectively. According to Levi-Donati et al. (1976), the meteorite mainly consists of olivine, pyroxene (ortho and monoclinic present) and FeNi phase, with less troilite. Accessory minerals include chromite, ilmenite and rare plagioclases. The occurrence of daubréelite was also reported by Melfi (1965) through X-ray analysis. However, due to oxidation, the occurrence of this phase is questionable. Mason (1967c) determined the olivine with Fa25 composition through X-ray analysis and optical microscopy. On the other hand, measures by Levi-Donati et al. (1976) indicated that the mineral was not homogeneous in composition and determined Fa20 and Fa25. Pyroxene also showed variation in its composition, ranging from Fs19 to Fs21, with an average of Fs20. Source: Gomes & Keil (1980).
CLASSIFICATION:
Mafra was classified in the chemical group H by Levi-Donati et al. (1976) based on the total chemistry and through the ratios Feº / Ni (8.79), Fe / SiO2 (0.70) and Feº / Fe (0.55), as well as the total concentration of total Fe in the meteorite (26.70%) and total FeNi of 16.48%. However, group L was suggested for the classification of the Mafra meteorite due to the composition of Fa25 olivine. The electron microprobe analyses for olivine and pyroxene are clearly consistent with group L. Thus, the total chemistry given by Levi-Donati el al. (1976) must be wrong, unless these analyses are of a non-representative portion of the entire meteorite and refer to a group H. The transitional petrographic classification of type 3-4, according to Van Schmus & Wood (1967) , is due to the texture with well-defined chondrules and the presence of glass, as well as by the mineralogy, with an abundance of twinned clinopyroxenes and scarcity of plagioclases. All clasts belong to the highest petrographic types from 4 to 5. Source: Gomes & Keil (1980).
CLASSIFIERS:
Not reported by the Meteoritical Bulletin Database. A preliminary description was carried out by Valarelli & Arruda (1965) and a more detailed study was published by Melfi (1965) and Levi-Donati et al. (1976). Source: Gomes & Keil (1980).
HISTORY:
The Mafra meteorite fell in the state of Santa Catarina in 1941 and was witnessed by several observers. In total, 4 individual fragments were collected by local residents. Source: Gomes & Keil (1980).
All information that does not have a specific source was extracted from the Meteoritical Bulletin Database.
All images are copyrighted.
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