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Abstract-Six large millimeter-to centimeter-size regions of one specimen of the Krymka LL3.1 ordinary chondrite show evidence of having been completely or nearly completely shock-melted in situ, a phenomenon rarely observed in primitive chondrites. The shock pressure, nominally in the range of 75-90 GPa, could only have been 30-35 GPa in a porous material like fine-grained matrix. The melted regions have an igneous texture and their silicates are zoned and unequilibrated. Large metal-troilite intergrowths formed in these regions. The metal has a nickel content corresponding to martensite and the troilite contains up to 4.2 wt% nickel. Melting must have been very short and cooling very fast (>100 °C/h at high temperature). The metal contains up to 0.7 wt% phosphorus. Abundant chromite crystals and sodium-iron phosphate glass globules are found in troilite. The differences in composition between the opaque phases found in the melted regions and those generally observed in unmetamorphosed chondrules are assigned to melting under closed system conditions. Surprisingly high Co concentrations (up to 13 wt%) were found in some metal grains in or at the periphery of melted regions. They likely resulted from sulfurization of metal by sulfur vapor produced during the shock. After solidification, at least one other shock led to mechanical effects in the melted regions.

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Abstract-Two dark lithic fragments and matrix of the Krymka LL3.1 chondrite were mineralogically and chemically studied in detail. These objects are characterised by the following chemical and mineralogical characteristics, which distinguish them from the host chondrite Krymka: (1) bulk chemical analyses revealed low totals (systematically lower than 94 wt%) due to high porosity; (2) enrichment in FeO and depletion in S, MgO and Si02 due to a high abundance of Fe-rich silicates and low sulfide abundance; (3) fine-grained, almost chondrule-free texture with predominance of a porous, cryptocrystalline groundmass and fine grains; (4) occurrence of a small amount of oncemolten material (microchondrules) enclosed in fine-grained materials; ( 5 ) occurrence of accretionary features, especially unique accretionary spherules; (6) high abundance of small calcium-aluminiumrich inclusions (CAIs) in one of the fine-grained fragments. It is suggested that the abundance of CAIs in this fragment is one of the highest ever found in an ordinary chondrite.Accretionary, fine-grained spherules within one of the fragments bear fundamental information about the initial stages of accretion as well as on the evolution of the clast, its incorporation, and history within the bulk rock of Krymka. The differences in porosity, bulk composition, and mineralogy of cores and rims of the fine-grained spherulitic objects allow us to speculate on the following processes: (1) Low velocity accretion of tiny silicate grains onto the surface of coarse metal or silicate grains in a dusty region of the nebula is the beginning of the formation of accretionary, porous (fluffy) silicate spherules. (2) Within a dusty environment with decreasing silicate/(metal + sulfide) ratio the porous spherules collected abundant metal and sulfide particles together with silicate dust, which formed an accretionary rim. Variations of the silicate/(sulfide + metal) ratio in the dusty nebular environment result in the formation of multi-layered rims on the surface of the silicate-rich spherules. (3) Soft accretion and lithification of rimmed, fluffy spherules, fine-grained, silicate-rich dust, metal-sulfide particles, CAIs, silicate-rich microchondrules, and coarse silicate grains and fragments followed. (4) After low-temperature processing of the primary, accretionary rock collisional fragmentation occurred, the fragments were subsequently coated by fine-grained material, which was highly oxidized and depleted in sulfides. ( 5 ) In a final stage this accretionary "dusty" rock was incorporated as a fragment within the Krymka host.

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