ordinary chondrite

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The most common of the three main classes of chondrite meteorites, and the most numerous of the observed falls. Ordinary chondrites consist of 10–15% (by volume) of fine-grained matrix material, 65–75% of chondrules (embedded in the matrix), and less than 1% of inclusions. The presence of chondrules, with diameters of 0.3–0.9 mm, in the ordinary chondrites shows that they have not been melted since they formed. The ordinary chondrites are divided into three subgroups on the basis of their content of iron and related elements, such as nickel. The H or high-iron group contains 25–30% iron; the L or low-iron group contains 20–25%; and the LL or low-iron, low-metal group contains only 18–20%. A substantial fraction of all three groups are impact breccias, resembling lunar breccias. The distinct chemistry of the three groups indicates that they originated from separate parent bodies. Each of the three subgroups may be further divided into a number of types on the basis of texture and mineralogy (e.g. H3, L6, and LL5).

Subjects: Astronomy and Astrophysics.

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