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Search and characterization of new types of extraterrestrial materials in meteorites

The aim of the project was to identify primitive extraterrestrial materials not represented in meteorite collections, to characterize their mineralogical, chemical, and possibly isotopic, composition, to try to understand the origin of the materials and consider the implications of these for early Solar System processes. These materials were looked for among "xenoliths" in meteorites, i.e. rock fragments or clasts enclosed in a meteorite but obviously different from the bulk material of the latter.
The search was carried out on samples of the Krymka chondrite because
- it is a "type 3", i.e. unmetamorphosed, chondrite, thought to have resided close to the surface of its parent-asteroid, and thus more susceptible to acquire foreign material than more deeply-sited meteorites;
- it has been shown by previous studies to contain such xenoliths;
- an exceptionally large amount of this meteorite is available in the Kiev collection, while this type of meteorite is usually quite small.

Three fine-grained clasts, included in the Krymka host, were studied in the course of this project. They are dark, FeO-rich, compositionally inhomogeneous, porous, and possibly carbon-rich. The three clasts have gross characteristic similar to each other and to previously described matrix lumps, but each one has also distinctive mineralogical features. Two of them are entirely devoid of chondrules. One of the fragments has an unusual and intriguing large-scale texture reminiscent of the chondritic texture. It is composed of densely-packed spheroidal objects surrounded by rims and embedded in a matrix. All three components (spherules, rims, matrix) are very fine-grained but they differ by their silicate/(sulfide + metal) ratio. Compared to the sherules, rims and matrix are remarkably enriched in sulfide and metal particles.
From both the chemical composition and the texture, it is inferred that one of the clasts is probably a piece of the Krymka matrix. It is just larger than usual. On the other hand, the two other objects are clearly fragments of rocks that were agglomerated before their incorporation into Krymka. Their very fine-grained texture and highly unequilibrated composition testify the primitive nature of their material. No known class of meteorite is made of such material. However, the presence of the clasts in Krymka indicates that there were places where or times when rocks accreted in the solar nebula, that were entirely devoid of chondrules, and made of fine-grained dust similar to the ordinary chondrite matrix.


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