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Rezumat articol ediţie STUDIA UNIVERSITATIS BABEÅž-BOLYAI
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Rezumat: The chondrites (stony meteorites) are believed to represent the oldest rocks in the solar system and they are characterized by the presence of small mineral spheres called chondrules. The chondrule texture represents one of the easier criteria used for the petrologic-chemical classification of all chondrite main categories (O -ordinary, E-enstatite, C-primitive/carbonaceous chondrites, Rumuruti -type and Kakangari -type meteorites).
Based on the metal content and mineralogical composition, the ordinary chondrites are subdivided into three distinct groups, designated as H, L, and LL chondrites. The H-chondrites have high iron content, about 25-31% (including 12-21% metallic iron), the L-chondrites have lower iron content, ranging from 20 up to 25% (with 5-10% metallic iron) and the LL-chondrites contain 19-22% iron (with only 2-3% metallic iron).
Six petrographic types of chondrites, numbered from 1 to 6, are recognized. The ordinary chondrites show four petrographic types (numbered from 3 to 6), indicating progressive stages of thermal metamorphism.
Based on texture, Van Schmus & Wood (1967) proposed 4 categories of chondrules for each chondrite petrographic type: very sharply defined chondrules (type 3; e.g. H3, L3, LL3), well-defined chondrules (type 4; i.g. H4, L4, LL4), readily distinguished chondrules (type 5; e.g. H5, L5, Ll5) and poorly defined chondrules (type 6; i.g. H6, L6, LL6). A fifth category (type 7), naming a melted type, was added (e.g. H7, L7, LL7).
Up to now, 7 fallen ordinary chondrites have been registered and investigated in Romania and various scientists previously classified them as follows: Mezö-Mădăraş (syn. Mădăraş) – L3, Ohaba – H5, Kakowa (syn. Cacova) – L6, Zsadany (syn. Jădani) – H5, Mocs (syn. Mociu) – L5-6, Sopot – H4, Tăuţi – L6. The single found ordinary chondrite, Tuzla, was classified as L6 type (Stanciu & Stoicovici, 1943; Graham et al., 1985; Miura et al., 1995; Iancu, 2003). ... |
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