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11 - Physical Components of Ordinary Chondrites

Published online by Cambridge University Press:  24 February 2026

Alan E. Rubin
Affiliation:
University of California, Los Angeles
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Summary

Chondrule types include porphyritic (FeO-poor and FeO-rich), barred olivine, radial pyroxene, granular, and cryptocrystalline. Chondrules in unequilibrated OC tend to have unfractionated refractory lithophile abundances; metallic components include one enriched in refractory siderophiles and one in common and volatile siderophiles. Although most chondrules are a few hundred µm in diameter, microchondrules (0.8-40 µm) and macrochondrules (0.5–5 cm) also occur. Compound chondrules include enveloping, sibling, and adhering varieties. Some chondrules have fine-grained rims, others igneous rims. Relict grains survived the most recent chondrule melting. Calcium–aluminum-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs) are very rare. Matrix material occurs mainly as chondrule rims and isolated lumps. Carbon-rich aggregates and clasts contain poorly graphitized C, amorphous C, metallic Fe-Ni, and minor chromite. A few H chondrites contain halite. Opaque assemblages include metallic Fe-Ni, sulfide, and oxides. Some shocked OC contain metallic Cu. Large metal nodules formed by impact-induced vaporization and fractional condensation. Many shocked OC exhibit silicate darkening, and many are breccias with a variety of clasts. Some OC are regolith breccias enriched in solar-wind-implanted noble gases.

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